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Cu- and Mn-bearing tourmalines from Brazil and Mozambique: Crystal structures, chemistry and correlations

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Cu- and Mn-bearing tourmalines from Brazil and Mozambique were characterised chemically (EMPA and LA-ICP-MS) and by X-ray single-crystal structure refinement. All these samples are rich in Al, Li and F (fluor-elbaite) and contain significant amounts of CuO (up to ~1.8 wt%) and MnO (up to ~3.5 wt%). Structurally investigated samples show a pronounced positive correlation between the distances and the (Li + Mn2+ + Cu + Fe2+) content (apfu) at this site with R 2 = 0.90. An excellent negative correlation exists between the distances and the Al2O3 content (R 2 = 0.94). The samples at each locality generally show a strong negative correlation between the X-site vacancies and the (MnO + FeO) content. The Mn content in these tourmalines depends on the availability of Mn, on the formation temperature, as well as on stereochemical constraints. Because of a very weak correlation between MnO and CuO we believe that the Cu content in tourmaline is essentially dependent on the availability of Cu and on stereochemical constraints.

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... The crystal structure of another Cu-bearing elbaite (with~1 wt.% CuO) from the same locality was refined by Ertl et al. (2002). Copper-and Mnbearing tourmalines from Brazil and Mozambique (up to~1.8 wt.% CuO and~3.5 wt.% MnO) were characterized chemically (EMPA and LA-ICP-MS) and by single-crystal structure refinement (Ertl et al. 2013). Eight structurally investigated samples showed a pronounced positive correlation between the <Y-O> distances and the (Li + Mn 2+ + Cu + Fe 2+ ) content (apfu) at this site with r 2 = 0.90 (Ertl et al. 2013). ...
... Copper-and Mnbearing tourmalines from Brazil and Mozambique (up to~1.8 wt.% CuO and~3.5 wt.% MnO) were characterized chemically (EMPA and LA-ICP-MS) and by single-crystal structure refinement (Ertl et al. 2013). Eight structurally investigated samples showed a pronounced positive correlation between the <Y-O> distances and the (Li + Mn 2+ + Cu + Fe 2+ ) content (apfu) at this site with r 2 = 0.90 (Ertl et al. 2013). An excellent negative correlation was also found by these authors between the <Y-O> distances and the Al 2 O 3 content (R 2 = 0.94). ...
... An excellent negative correlation was also found by these authors between the <Y-O> distances and the Al 2 O 3 content (R 2 = 0.94). Ertl et al. (2013) concluded that within the analytical errors Cu and Mn 2+ occupy only the [6]-coordinated Y site. Vereshchagin et al. (2013) gave the chemistry (EMPA, light elements were calculated) and singlecrystal structure refinement of three Cu-bearing tourmalines (two natural samples:~1.6 wt.% and 3.5 wt.% CuO; synthetic sample:~8.4 ...
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A synthetic Cu-rich tourmaline crystal (Lebedev et al. 1988) consists of three different zones. Each zone was characterized by EMPA, SIMS, and single-crystal structure refinement (SREF). The first zone (which crystallized directly on the seed crystal) has the formula ~X(Na0.8□0.2) Y(Al2.0Cu0.9□0.1) ZAl6 T(Si5.1Al0.9)O18 (BO3)3 V(OH)3 W[O0.7F0.2(OH)0.1] with lattice parameters a 15.835(1), c 7.093(1) Å (R = 2.4%). The second zone has the formula ~X(Na0.8□0.2) Y(Al1.8Cu1.1□0.1) ZAl6 T(Si5.1Al0.7B0.2)O18 (BO3)3 V(OH)3 W[(OH)0.4F0.3O0.3] with a 15.824(1), c 7.087(1) Å (R = 2.3%). The third zone (highest Cu content with ~14 wt.% CuO) has the formula X(Na0.81□0.19) Y(Cu1.72Al1.21□0.07) Z(Al5.96Cu0.04) (BO3)3 T(Si5.17Al0.48B0.35)O18 V(OH)3 W[(OH)0.63F0.37] with a 15.849(1), c 7.087(1) Å (R = 2.5%). While [4]Al decreases from zone 1 to zone 3, [4]B increases (by chemistry and SREF), which could be explained by a decreasing temperature during tourmaline crystallization. Such a T-site occupancy is in agreement with the <T–O> distance, which strictly monotonically decreases from 1.625(1) to 1.616(1) Å. We suggest that very small amounts of Cu are present at the Z site of all investigated tourmaline samples, but only in the Cu-richest zone (~14 wt.% CuO) is the refined value for Cu at the Z site (~1% of the total Cu)higher than the 3σ error. The YO6 octahedron of this Cu-richest known tourmaline is mainly occupied by Cu. Two of the six (Cu,Al)–O distances are significantly enlarged: Y–O1 with 2.031(2) Å and Y–O3 with 2.170(2) Å, while the other distances Y–O2 and Y–O6 with ~1.951(2) Å are significantly smaller. The proportion of the average of the two enlarged distances to the average of the other distances in the Cu-richest zone gives a value of ~1.08, which is the highest value known so far for Cu-bearing tourmalines. We conclude that for the Cu-richest zone the Jahn-Teller effect appears to be verified.
... In addition, B, Li and several trace elements, including rare-earth elements (REE), were analysed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to obtain a comprehensive picture of the composition of these tourmalines. Analytical data on 15 additional, partly unpolished, crystals from Brazil (BRA20-BRA28) and Mozambique (MOZ19-MOZ24) were presented in an article that focused on the structural refinement of these tourmalines (Ertl et al., 2013); they generally show a strong negative correlation between X-site vacancy and Mn+Fe content. Ertl et al. (2013) concluded that the Mn content in such tourmaline depends on the geochemical availability of Mn and the formation temperature, as well as on stereochemical constraints. ...
... Analytical data on 15 additional, partly unpolished, crystals from Brazil (BRA20-BRA28) and Mozambique (MOZ19-MOZ24) were presented in an article that focused on the structural refinement of these tourmalines (Ertl et al., 2013); they generally show a strong negative correlation between X-site vacancy and Mn+Fe content. Ertl et al. (2013) concluded that the Mn content in such tourmaline depends on the geochemical availability of Mn and the formation temperature, as well as on stereochemical constraints. Because of a very weak correlation between MnO tot and CuO, they argued that the Cu content in tourmaline is essentially dependent on the geochemical availability of Cu and on stereochemical constraints. ...
... OH and O were calculated by using the empirical formulae OH = 3+(1-F)/2 and O = 31-(F+OH) of Grice and Ercit (1993). Li 2 O was calculated based on the assumptions that (1) Si = 6 apfu, (2) Al on the tetrahedral position is negligible (Ertl et al., 2013) and (3) the Y position is completely filled with 3 apfu. Because there is no indication of tetrahedrally coordinated B, the B 2 O 3 content was calculated with the assumption that the B site is completely filled with 3 apfu. ...
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Copper-bearing tourmalines are highly prized for their vivid coloration. We analysed the major and trace elements of some gem-quality Cu-bearing tourmalines (e.g. blue, greenish blue, yellowish green, green, violet and pink) from Brazil, Mozambique and Nigeria. Most of them contained significant amounts of Cu, Mn or a combination of both elements. There was no clearcut correlation of the Cu and Mn contents with coloration. Blue colour was in most cases due to Cu²⁺. Pink and violet coloration (due to Mn³⁺) was shown by Mn-bearing tourmalines that contained no significant Fe. Green colour in the Nigerian tourmaline was most probably due to a combination of Mn, Cu and Fe. Some of the green samples from Brazil contained up to 0.6 wt.% V2O3. Among the trace elements, remarkable contents of Pb (up to 4,000 ppm) and Bi (up to 2,900 ppm) were detected rarely in samples from all three countries. Based on a comparison of unheated pink and violet samples with data for blue Paraíba-type tourmalines, CuO/MnOtot is usually ≥0.5 for unheated blue samples. Hence, we suggest that blue Cu-bearing tourmalines with CuO/MnOtot <0.5 may have been heat treated to reduce the contribution of the reddish component of Mn³⁺.
... They represent hydroxyl-, fluor-and oxy-species of X-site vacant, alkali, and calcic tourmalines with typical octahedral occupants like Fe 2+ , Mg 2+ , Mn 2+ , Al 3+ , Li + , Fe 3+ , Cr 3+ , and V 3+ . Crystal-chemical relations in the tourmaline supergroup and the crystal chemistry of tourmalinesupergroup minerals have been investigated by many authors in the last 50 years (e.g., Donnay and Barton 1972;Povondra and Čech 1976;Deer et al. 1986;Foit 1989;Hawthorne et al. 1993;Hawthorne 1996Hawthorne , 2002Hawthorne , 2016Henry and Dutrow 1996;Bloodaxe et al. 1999;Ertl et al. 2002Ertl et al. , 2012aErtl et al. , 2012bErtl et al. , 2013Ertl et al. , 2015Ertl et al. , 2018Hughes et al. 2011;Lucchesi 2004, 2007;Bosi et al. , 2013Bosi et al. , 2015Bosi et al. , 2017Ertl and Tillmanns 2012;Ertl and Bačík 2020;Bačík and Fridrichová 2021). Tourmaline can also be a petrologic recorder of its geologic history as was demonstrated by Van Hinsberg et al. (2011). ...
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Alumino-oxy-rossmanite, ideally ☐Al3Al6(Si5AlO18)(BO3)3(OH)3O, is here described as a new member of the tourmaline supergroup. It is an early magmatic Al-rich oxy-tourmaline from a small pegmatitic body embedded in amphibolite and biotite-rich paragneiss. This new pink tourmaline was found in a Moldanubian pegmatite (of the Drosendorf Unit) that occurs in a large quarry near the village of Eibenstein an der Thaya, Waidhofen an der Thaya district, Lower Austria, Austria. The empirical formula of the holotype was determined on the basis of electron microprobe analysis (EMPA), secondary ion mass spectrometry (SIMS), spectroscopical methods (optical absorption and infrared spectroscopy), and crystal-structure refinement (SREF) as X(☐0.53Na0.46Ca0.01) Y(Al2.37Mn0.213+Li0.16☐0.14Mn0.072+Fe0.033+Fe0.012+Ti0.014+) ZAl6(Si5.37Al0.41B0.22O18)(BO3)3V[(OH)2.77O0.23] W[O0.80(OH)0.15F0.05]. Chemical composition (wt%) is: SiO2 33.96, TiO2 0.10, Al2O3 47.08, B2O3 11.77, FeO 0.08, Fe2O3 0.23, MnO 0.52, Mn2O3 1.70, CaO 0.04, Li2O 0.25, ZnO 0.03, Na2O 1.51, H2O 2.79, F 0.09, total 100.11. The presence of relatively high amounts of trivalent Mn in alumino-oxy-rossmanite is in agreement with the observation that the OH groups are present at a lower concentration than commonly found in other Al-rich and Li-bearing tourmalines. The crystal structure of alumino-oxy-rossmanite [space group R3m; a = 15.803(1), c = 7.088(1) Å; V = 1532.9(3) Å3] was refined to an R1(F) value of 1.68%. The eight strongest X-ray diffraction lines in the (calculated) powder pattern [d in Å (I) hkl] are: 2.5534 (100) 051, 3.9508 (85) 220, 2.9236 (78) 122, 4.1783 (61) 211, 2.4307 (55) 012, 2.0198 (39) 152, 1.8995 (30) 342, 6.294 (28) 101. The most common associated minerals are quartz, albite, microcline, and apatite. Beryl and, in places, schorl are also found as primary pegmatitic phases. Because of the low mode of associated mica (muscovite), we assume that the silica melt, which formed this pegmatite, crystallized under relatively dry conditions, in agreement with the observation that alumino-oxy-rossmanite contains a lower amount of OH than most other tourmalines. This new member of the tourmaline supergroup exhibits the most Al-rich end-member composition of the tourmaline supergroup (theoretical content: ~54 wt% Al2O3). The significant content of tetrahedrally coordinated Al could reflect the relatively high-temperature conditions (~700 °C) inferred for crystallization of the pegmatite. Alumino-oxy-rossmanite was named for its chemical relationship to rossmanite, ☐(LiAl2)Al6(Si6O18) (BO3)3(OH)3(OH), which in turn was named after George R. Rossman, Professor of Mineralogy at the California Institute of Technology (Pasadena, California, U.S.A.).
... We analyzed data on 45 tourmalines containing trivalent cations (Me 3+ : Cr 3+ , V 3+ , Fe 3+ ; Tables S1-S6 in Supplementary Material linked to this article and freely available at https://pubs.geoscienceworld.org/eurjmin, including data from Bloodaxe et al., 1999;Bosi, 2008;Bosi et al., , 2005Bosi et al., , 2012Bosi et al., , 2013aBosi et al., , 2013bBosi et al., , 2014Bosi et al., , 2017aCámara et al., 2002;Cempírek et al., 2013;Ertl et al., , 2016aGorskaya, 1985;MacDonald & Hawthorne, 1995b;Peltola et al., 1968;Pertlik et al., 2003;Rozhdestvenskaya et al., 2012;Vereshchagin et al., 2014) and 43 tourmalines containing divalent cations (Me 2+ : Fe 2+ , Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ ; Tables S7-S14 in Supplementary Material, including as additional data sources Aurisicchio et al., 1999;MacDonald et al., 1993;Burns et al., 1994;MacDonald & Hawthorne, 1995a;Lussier et al., 2001;Ertl et al., 2002Ertl et al., , 2003Ertl et al., , 2006Ertl et al., , 2010Ertl et al., , 2013Ertl et al., , 2015Ertl et al., , 2016bCempirek et al., 2006;Hughes et al., 2011;Bosi et al., 2012aBosi et al., , 2015Bosi et al., , 2017bVereshchagin et al., 2013Vereshchagin et al., , 2015Vereshchagin, 2016). ...
Article
The crystal structure of 45 tourmalines containing trivalent cations (Me³⁺:Cr³⁺,V³⁺,Fe³⁺) and 43 tourmalines containing divalent cations (Me²⁺:Fe²⁺,Mn²⁺,Co²⁺,Ni²⁺,Cu²⁺) of 3d elements were analysed. We establish that the incorporation of Me³⁺ cations is controlled by the ratio between the sizes of YO6 and ZO6 octahedra and does not exceed eight atoms per formula unit (apfu), while the incorporation of Me²⁺ cations is controlled by the charge balance and does not exceed 3 apfu. We prove that there are no structural constraints controlling the incorporation of Co, Ni and Cu cations into the tourmaline structure at concentrations of up to 1 apfu. We show that, when the limiting content (less or equal to 1 apfu and 1.6 apfu for divalent and trivalent cations, respectively) is reached, these cations start to occupy not only YO6, but also ZO6 octahedra, to maintain stability of the crystal structure. As the content of 3d-element cations increases further, the degree of disorder grows and, at a content of ~7 apfu, their distribution is close to statistical. An increase in the content of 3d cations, accompanied by their disordering, causes a decrease in disparity between sizes of YO6 and ZO6 octahedra and their deformations. © 2018 E. Schweizerbart’sche Verlagsbuchhandlung, 70176 Stuttgart, Germany.
... The presence of a large number of substitutional atoms and vacancies involves additional complexity in the tourmaline structure [39,40] resulting in a great number of endmember minerals, such as schorl [NaFe3Al6(BO3)3Si6O18(OH)4], dravite [NaMg3Al6(BO3)3Si6O18(OH)4], elbaite [Na(Li,Al)3Al6(BO3)3Si6O18(OH)4] (whose red variety is known as rubellite), buergerite [NaFe 3+ 3Al6(BO3)3Si6O18(O,F)4], uvite [(Ca,Na) (Mg,Fe)3Al5Mg(BO3)3Si6O18(OH,F)4], hydroxyuvite, liddicoatite, olenite, chromdravite, vanadiumdravite, foitite, magnesiofoitite, feruvite, povondraite and rossmanite (the ideal chemical formulae of the most common ones are given). In the meantime, numerous papers related to the crystal structure study of various types of tourmaline have been published in the literature [41][42][43][44][45][46][47]. ...
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p>A review of the results of the complementary use of vibrational spectroscopy (infrared and Raman) and X-ray powder diffraction in the process of identification and spectra–structure correlation of some cyclo-, phyllo- and tectosilicate minerals originating from the Republic of Macedonia is presented. The following minerals are studied: schorl, Na(Fe<sup>2+</sup>,Mg)<sub>3</sub>Al<sub>6</sub>(BO<sub>3</sub>)<sub>3</sub>Si<sub>6</sub>O<sub>18</sub>(OH)<sub>4</sub>; beryl, (Be,Mg)<sub>3</sub>Al<sub>2</sub>Si<sub>6</sub>O<sub>18</sub>; chrysotile, Mg<sub>3</sub>Si<sub>2</sub>O<sub>5</sub>(OH)<sub>4</sub>; antigorite, (Mg,Fe<sup>2+</sup>)<sub>3</sub>Si<sub>2</sub>O<sub>5</sub>(OH)<sub>4</sub>; talc, (Mg,Fe<sup>2+</sup>)<sub>3</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub>; clinochlore, (Mg,Fe<sup>2+</sup>)<sub>5</sub>Si<sub>3</sub>(Al,Cr)<sub>2</sub>O<sub>10</sub>(OH)<sub>8</sub>; cymrite, BaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub>×H<sub>2</sub>O; mont­morillonite, (K,Ca)<sub>0.3</sub>(Al,Mg)<sub>2</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub>×nH<sub>2</sub>O; muscovite, KAl<sub>2</sub>(Si<sub>3</sub>Al)O<sub>10</sub>(OH,F)<sub>2</sub>; phlogopite, KMg<sub>3</sub>(Si<sub>3</sub>Al)O<sub>10</sub>(OH,F)<sub>2</sub>; biotite, K(Mg,Fe<sup>2+</sup>)<sub>3</sub>AlSi<sub>3</sub>O<sub>10</sub>(OH,F)<sub>2</sub>; sheridanite, (Mg,Al)<sub>6</sub>(Si,Al)<sub>4</sub>O<sub>10</sub>(OH)<sub>8</sub>; albite, NaAlSi<sub>3</sub>O<sub>8</sub>; microcline, KAlSi<sub>3</sub>O<sub>8</sub>; sanidine, (K,Na)(Si,Al)<sub>4</sub>O<sub>8</sub> and stilbite, Na<sub>3</sub>Ca<sub>3</sub>Al<sub>8</sub>Si<sub>28</sub>O<sub>72</sub>×30H<sub>2</sub>O.</p
... 3), the three doublets from dark green and light green tourmaline spectra were ascribed to Fe 2+ at Y site with different nearest-neighbor coordination environments (following Dyar et al. 1998;Pieczka et al. 1998;Castañeda et al. 2006b;Andreozzi et al. 2008). This interpretation agrees with various structure refinement studies performed on Li-bearing tourmalines which showed that the Z site is typically fully populated by Al (e.g., Bosi et al. 2013;Ertl et al. 2013). ...
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This study characterizes natural black, blue, dark green, light green and pink tourmalines from granitic pegmatites of the Mata Azul Pegmatitic Field in central Brazil. The differences were assessed by applying electron-microprobe analysis as well as Mössbauer and optical spectroscopies. Mineral chemistry data show an increasing Mn/(Mn + Fe) atomic ratio as follows: black (0.01–0.02), blue (0.04–0.05), dark green (0.09–0.21), light green (0.33–0.42) and pink (0.68–1.00). The Mössbauer spectroscopy results show the presence of Fe ²⁺ (doublets with isomer shift (δ): 1.04–1.15 mm/s) for the black, blue, light green and dark green tourmalines. Fe ²⁺ is found in three different environments that are identified by quadrupole splitting (Δ) of 2.38–2.49 mm/s for the first, Δ = 2.13–2.34 mm/s for the second, and Δ = 1.54–1.71 mm/s for the third. The black sample spectrum has an additional fourth doublet (δ = 0.78 mm/s, Δ = 1.22 mm/s) that is assigned to an electron delocalization between Fe ²⁺ and Fe ³⁺ . In the studied samples, the black color results most likely from high absorbance in all the visible spectra caused by Fe ²⁺ –Fe ³⁺ intervalence charge transfer (IVCT) (780 nm), Fe ²⁺ d–d transitions (730 nm, 670 nm), Fe ²⁺ –Ti ⁴⁺ IVCT (430 nm) and transitions related to Mn cations (550 nm). Blue is differentiated from green colors by a higher absorbance in the 730 nm region (Fe ²⁺ d–d transitions), and a higher FeO content, as well as a lower absorbance in the 430 nm region and a lower TiO 2 content. The green colors are associated with the absorption bands at 730 nm (Fe ²⁺ d–d transitions) and 430 nm (Fe ²⁺ –Ti ⁴⁺ IVCT). The light green color exhibited a lower intensity of these bands compared to that of the dark green color, and an additional band at 320 nm (Mn ²⁺ –Ti ⁴⁺ IVCT). The pink color results from the high degree of Mn–Fe fractionation but it was not possible to assure the oxidation states of the Mn cations.
... The crystallography of tourmaline-supergroup minerals enables to accommodate a wide range of major, minor, and trace elements in the structure and causes isovalent and coupled substitutions (e.g., Foit Jr. and Rosenberg, 1977;Gallagher, 1988;Burt, 1989;Henry and Dutrow, 1990, 2001Kazachenko et al., 1993;London and Manning, 1995;Jiang et al., 2004;Baksheev and Kudryavtseva, 2004;Buriánek and Novák, 2007;Arif et al., 2010;Yavuz et al., 2011;Ertl et al., 2013). These substitution mechanisms that make the tourmaline crystal chemistry difficult to characterize are used in different binary plots to reveal the specific features of tourmaline composition. ...
... (Grice et al. 1993). Values for the other natural tourmalines are from: Ertl et al. (2006Ertl et al. ( , 2007Ertl et al. ( , 2008aErtl et al. ( , 2008bErtl et al. ( , 2009Ertl et al. ( , 2010aErtl et al. ( , 2010bErtl et al. ( , 2010cErtl et al. ( , 2012aErtl et al. ( , 2012bErtl et al. ( , 2013Ertl et al. ( , 2016aErtl et al. ( , 2016b, Bosi (2008), Lussier et al. (2008Lussier et al. ( , 2011aLussier et al. ( , 2011bLussier et al. ( , 2016, Bosi et al. (2010Bosi et al. ( , 2012Bosi et al. ( , 2013aBosi et al. ( , 2013bBosi et al. ( , 2013cBosi et al. ( , 2014aBosi et al. ( , 2014bBosi et al. ( , 2015aBosi et al. ( , 2015bBosi et al. ( , 2015cBosi et al. ( , 2016aBosi et al. ( , 2016bBosi et al. ( , 2017aBosi et al. ( , 2017c, Clark et al. (2011), Filip et al. (2012, Gatta et al. (2012), , Bačík et al. (2013Bačík et al. ( , 2015, Novák et al. (2013), Reznitskii et al. (2014), and Grew et al. (2018). Values for the synthetic tourmalines are from Berryman et al. (2016b) and Kutzschbach et al. (2016). ...
... in the X-site for liddicoatites, they are easily distinguished based on major element analyses. Cu 2+ in copper-bearing tourmaline is considered to be located in the Y-site (e.g., Ertl et al., 2013). The normalization method established by Sun et al. (2019) allows for the accurate calculation of tourmaline stoichiometry from LA-ICP-MS analyses, with the exception of the fluor-and oxy-species. ...
Chapter
Silicate minerals, including quartz, play a pivotal role in the make-up of planet Earth.
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Zinc-rich fluor-elbaite from Piława Górna, Poland, was studied by electron microprobe (EPMA), single-crystal X-ray diffraction (SREF), and Raman spectroscopy (RS) to check the possibility of the application of RS to draw crystal-chemical conclusions for Al-rich and Li-bearing tourmalines on basis of the O–H stretching vibrations in the spectral range 3400–3800 cm–1. This tourmaline, forming a thin metasomatic zone around gahnite, features varying compositions with a ZnO content reaching in the studied fragment of 5.70(12) wt%. The crystal structure of this Zn-rich fluor-elbaite [a = 15.921(1), c = 7.127(1) Å] was refined with a R1 value of 1.67%. Its formula was determined on the basis of electron-microprobe and structure refinement as (Na0.84☐0.14Ca0.01)XΣ1.00(Al1.06Li0.84Zn0.69Fe0.322+Mn0.09)YΣ3.00AlZ6(BO3)3(Si6TO18)(OH)3V(F0.65OH0.26O0.09)W. The deconvolution of the O–H stretching vibration bands, performed by fitting of an input model of component bands with Gaussian function shapes for the empirical spectrum, indicates that each of the three maxima assigned for VOH bonded to YAl3+, Y2+, and YLi+ and with the total integral intensity of at least 75% of the total OH content could be resolved into 1 to 3 bands, depending on the X-site occupation (vacancies, Na+, and Ca2+). The deconvolution indicates further that several low intense bands of WO–H modes above a Raman shift of 3600 cm–1, totally reaching ≤25%, are dependent on the occupation of triplets of YYY cations bonded to the hydroxyl. These WO–H modes are also influenced by the X-site occupation. Due to ordering of all octahedral cations (except Al) at the Y site and a complete occupation of the Z site by Al and the V site by OH, it seems possible to evaluate the Li and OH contents in a Al-rich and Li-bearing tourmaline directly from the Raman spectrum. By using the ratio VOHIYAlZAlZAl/(VOHIYZZ + WOHIYYY) as evaluated from RS, corresponding to the ratio YAl/V+WOH in the crystal, the formula of the Zn-rich fluor-elbaite can be calculated as (Na0.85☐0.14Ca0.01)XΣ1.00(Al1.11Y1.112+Li0.78)YΣ3.00AlZ6(BO3)3(Si6O18)(OH)3(F0.65OH0.13O0.22), where Y 2+ = Zn + Fe + Mn. The formula, determined only on basis of EPMA and deconvolution of RS in the O–H stretching bands, corresponds very well (≤1 SD range of EPMA) to the formula determined on basis of EPMA and SREF. This result implicates that the O–H stretching vibrations, measured by Raman spectroscopy, could be applied for Al-rich and Li-bearing tourmalines as a useful tool for providing additional information for determining the crystal-chemical formula. It is also very helpful when crystal structural data are not available.
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Six Al- and Li-bearing tourmaline crystals from pegmatites were structurally and chemically characterized. These samples can be assigned to elbaite, fluor-elbaite and rossmanite. Quantitative analyses of light elements such as Li, B and H are not always easily accessible. Therefore a method for the calculation of Li and OH would be of a general interest for the Geosciences. In the present work we test whether relatively accurate Li and OH estimations are possible based on the deconvolution of the O–H stretching vibration modes in a Raman spectrum on common (Al,Li)-rich tourmalines. We use the short-range arrangement model in our band interpretation as this model, in contrast to other models, provides the ability to evaluate an additional parameter by analyzing the OH stretching modes that can be used in the formula calculation process, which ultimately leads to the estimation of Li and OH with high accuracy. We also compare microprobe and Raman spectroscopy results, which we combine, with optimized data derived from microprobe and single-crystal structure refinement by using the same crystals. Based on our investigations, where the Raman spectra were recorded on non-oriented crystal sections, we conclude that we produce more accurate estimations, when the effects of the section orientation are considered. Therefore, we also propose a new method to correct the influence of the orientation of the crystal section.
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In the present paper, I report on the spectroscopic study for tourmaline color origin, performed red samples from Minas Geras State, Brazil, by gemological routine testing, X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, and X-ray photoelectron spectroscopy. The main goal was the analysis of the optical absorption spectra and the chemical states of transition metal cations in order to better understand the effect of transition metal cations on color of tourmaline. The results showed that the red color was confirmed by the symmetric broad absorption at 527 nm and the narrow absorption at 400 and 450 nm, and the above three absorption bands were caused by the d-d electron transition of Mn3+, which occupied the Y site in the crystal structure and coordinated with F to form bonds. In addition, in principle, the chemical states of the chromogenic ions in tourmaline and their influence on coloration were confirmed, which would be beneficial to assessing the color change and identifying the origin of tourmaline.
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In this paper we have presented a detailed response to Ertl et al. (2012a) who, in a paper in volume 97 (year 2012), pages 1402-1416, this journal, claim evidence for limitations of Fe2+ and Mn2+ occupancy at the Z site of the tourmaline structure. They also propose a model by which the distance of tourmaline varies as a function of its and bond lengths. We have examined their conclusions and find that a different distribution of cations over the Y and Z sites gives better agreement with the extensive experimental information available. In fact, on the basis of crystal-structure refinements, Mossbauer spectroscopy, optical absorption spectroscopy, bond-valence theory, ionic radius concept and literature, the occurrence of Fe2+ at the Z site of tourmaline is well supported. Conversely, existing experimental data does not provide indisputable evidence for the occurrence of Mn2+ at the Z site. Despite this, there is no evidence for inductive effects of Mn-Y(2+) on , and the proposed effects must be regarded as speculative. Statistical analysis shows that the average value is 1.906(2) angstrom, which is consistent with the observed values of at the 99% confidence limit (within 3) in tourmalines with the Z site fully occupied by Al. Consequently, the proposed inductive effect of and on can be ruled out.
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High-pressure single-crystal X-ray diffraction patterns on five synthetic Mg-Al tourmaline of near end-member composition (dravite NaMg3Al6Si6O18(BO3)3(OH)3OH, K-dravite KMg3Al6Si6O18(BO3)3(OH)3OH, magnesio-foitite ☐(Mg2Al)Al6Si6O18(BO3)3(OH)3OH, oxy-uvite CaMg3Al6Si6O18(BO3)3(OH)3O, and olenite NaAl3Al6Si6O18(BO3)3O3OH, where ☐ represents an X-site vacancy) were collected to 60 GPa at 300 K using a diamond-anvil cell and synchrotron radiation. No phase transitions were observed for any of the investigated compositions. The refined unit-cell parameters were used to constrain 3rd-order Birch-Murnaghan pressure-volume equation of states with the following isothermal bulk moduli (K0 in GPa) and corresponding pressure derivatives (K0’= ∂K0/∂P)T: dravite K0=97(6), K0’=5.0(5); K-dravite K0=109(4), K0’= 4.3(2); oxy-uvite K0=110(2), K0’=4.1(1); magnesio-foitite K0=116(2), K0’=3.5(1); olenite K0=116(6), K0’=4.7(4). Each tourmaline has highly anisotropic behavior under compression, with the c axis 2.8 - 3.6 times more compressible than the a axis at ambient conditions. This anisotropy decreases strongly with increasing pressure and the c axis is only ~14% more compressible than the a axis near 60 GPa. The octahedral Y- and Z-sites’ composition exerts a primary control on tourmaline’s compressibility, whereby Al content is correlated with a decrease in the c-axis compressibility and a corresponding increase in K0 and K0’. Contrary to expectations, the identity of the X-site-occupying ion (Na, K, or Ca) does not have a demonstrable effect on tourmaline’s compression curve. The presence of a fully vacant X site in magnesio-foitite results in a decrease of K0’ relative to the alkali and Ca tourmalines. The decrease in K0’ for magnesio-foitite is accounted for by an increase in compressibility along the a axis at high pressure, reflecting increased compression of tourmaline’s ring structure in the presence of a vacant X site. This study highlights the utility of synthetic crystals in untangling the effect of composition on tourmaline’s compression behavior.
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Considerable uncertainty has surrounded the occurrence of tetrahedrally coordinated Al and B at the T site in tourmaline. Although previously detected in several tourmaline specimens, the frequency of these substitutions in nature, as well as the extent to which they occur in the tourmaline structure, is not known. Using 11 B and 27 Al MAS NMR spectroscopy, we have investigated the presence of B and Al at the T site in 50 inclusion-free tourmaline specimens of low transition-metal content and different species (elbaite, "fluor-elbaite," liddicoatite, dravite, uvite, olenite, and magnesiofoitite) from different localities worldwide. Chemical shifts of [4] B and [3] B in 11 B spectra, and [4] Al and [6] Al in 27 Al spectra, are well resolved, allowing detection of even small amounts of T-site constituents. In the observed spectra, [4] B and [3] B peaks are located at 0 and 18-20 ppm, respectively, with the greatest intensity corresponding to [3] B (=3 apfu). In 27 Al spectra, [4] Al and [6] Al bands are located at 68-72 and 0 ppm, respectively, with the greater intensity corresponding to [6] Al. However, inadequate separation of Y Al and Z Al precludes resolution of these two bands. Simulation of 11 B MAS NMR spectra shows that tetrahedrally and trigonally coordinated B can be readily distinguished at 14.1 T and that a [4] B content of 0.0-0.5 apfu is common in tourmaline containing low amounts of paramagnetic species. 27 Al MAS NMR spectra show that Al is also a common constituent of the T site in tourmaline. Determination of [4] Al content by peak-area integration commonly shows values of 0.0-0.5 apfu. Furthermore, the chemical shift of the 27 Al tetrahedral peak is sensitive to local order at the adjacent Y and Z octahedra, where [4] Al-Y Mg 3 and [4] Al-Y (Al,Li) 3 arrangements result in peaks located at ~65 and ~75 ppm, respectively. Both 11 B MAS NMR and 27 Al MAS NMR spectra show peak broadening as a function of transition-metal content (i.e., Mn 2+ + Fe 2+ = 0.01-0.30 apfu) in the host tourmaline. In 11 B spectra, broadening and loss of intensity of the [3] B signal ultimately obscures the signal corresponding to [4] B, increasing the limit of detection of [4] B in tourmaline. Our results clearly show that all combinations of Si, Al, and B: T = (Al, Si) 6 , T = (B, Si) 6 , T = (Al, B, Si) 6 , and T = Si 6 apfu, are common in natural tourmalines.
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The crystal structures of 23 samples extracted from a large slice oriented along (001) of a single crystal of liddicoatite from the Anjanabonoina granitic pegmatite in Madagascar (showing pronounced, visually discontinuous oscillatory zones and anomalous biaxiality) were refined to R1 indices of 1.5-2.9% (<R 1 > = 1.78%). Cell parameters are in the range a ≈ 15.82-15.87, c ≈ 7.10-7.12 Å. Spindle-stage measurement of 2V gave values of 0.0° for a fragment from the (001) zone and 8(3) and 18.9(5)° for fragments from the pyramidal zone of the crystal. However, single-crystal X-ray intensity data show no deviation from 3m Laue symmetry, indicating that there is no information in the diffraction data on any deviation from R3m symmetry. The distances are in the range 1.616-1.619 Å, with a grand mean value of 1.6175(7) Å. The occupancy of the T site was expressed as xSi + (1-x)B, and x was treated as variable in the refinement procedure. The effect of using different scattering factors (i.e., ionized versus neutral) on the refined site-occupancies was investigated in detail. The grand mean refined [4] B content of the T site varies from-0.04 apfu for ionized scattering-curves for O and Si to 0.25 apfu for neutral scattering-curves for O and Si, illustrating the effect of the use of different scattering curves on refined [4] B site-populations. Examination of distances as a function of aggregate cation radius for tourmalines containing [4] B and [4] Al shows a large amount of scatter, emphasizing the need for more accurate data. The limits of detection for 11 B and 27 Al in tourmaline by Magic-Angle-Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy were investigated by simulation. For minimum (<0.04 apfu) and maximum (0.12 apfu) contents of (paramagnetic) transition metals, the limits of detection of [4] B are ~0.02 and 0.08 apfu, and of [4] Al are ~0.01 and 0.01 apfu, respectively. 11 B and 27 Al MAS NMR spectroscopy gave no evidence of the presence of tetrahedrally coordinated B or Al at the T site above these detection limits in any sample. This result is in accord with our refinement results using an ionized scattering-curve for O and a neutral scattering-curve for Si, suggesting that use of these curves is giving more accurate results than refinement with neutral scattering factors. The distances are in the range 1.904-1.907 Å, with a grand mean value of 1.9047(8) Å, and structure refinement indicates site-scattering values in accord with complete occupancy of the Z site by Al. Hence throughout this complexly zoned crystal, Si = 6.00 apfu and Z Al = 6.00 apfu. SommAIrE Nous décrivons la structure cristalline de 23 fragments extraits d'une section orientée le long de (001) d'un monocristal de liddicoatite provenant de la pegmatite granitique d'Anjanabonoina, au Madagascar, et affinés jusqu'à un résidu R1 dans l'intervalle 1.5-2.9% (<R 1 > = 1.78%). Ce cristal montre des zones oscillatoires discontinues et une biaxialité anomale. Les paramètres réticulaires ont des valeurs dans les intervalles suivants: a ≈ 15.82-15.87, c ≈ 7.10-7.12 Å. Les mesures de 2V utilisant ces fragments sur tige orientable ont donné des valeurs de 0.0° pour un fragment provenant de la zone (001), et 8(3) et 18.9(5)° pour des fragments pris de la zone pyramidale. Toutefois, les données portant sur les intensités en diffraction X ne révèlent aucune déviation de la symétrie de Laue 3m, ce qui montre qu'il n'y a aucune information concernant un écart de la symétrie R3m dans ces données. Les distances tombent dans l'intervalle 1.616-1.619 Å, avec une moyenne globale de 1.6175(7) Å. L'occupation du site T est exprimée sous forme xSi + (1-x)B, et nous avons traité x comme une variable au cours des affinements. Le fait d'utiliser des facteurs de dispersion différents, c'est-à-dire des facteurs prévus pour des atomes neutres § E-mail address: frank_hawthorne@umanitoba.ca 64 THE CAnADIAn mInErALoGIST ou des ions, exerce une influence sur les occupations affinées des sites. La teneur moyenne globale en [4] B des sites T varie de-0.04 apfu pour des facteurs d'atomes O et Si ionisés à 0.25 apfu en adoptant des facteurs de dispersion pour les atomes O et Si neutres, illustration de l'importance de ces facteurs sur la quantité de [4] B qui est affinée. Un examen des distances en fonction des rayons regroupés des cations dans les tourmalines contenant [4] B et [4] Al montre de grands écarts, et démontre la nécessité d'obtenir des données plus justes. Les limites de détection de 11 B et 27 Al dans une tourmaline par résonance magnétique nucléaire et spin à l'angle magique ont été étudiées avec des spectres simulés. Pour des teneurs minimales et maximales des métaux de transition (paramagnétiques), <0.04 et 0.12 apfu, les limites de détection du [4] B seraient entre ~0.02 et 0.08 apfu, et celles du [4] Al, entre ~0.01 et 0.01 apfu, respectivement. La spectroscopie MAS NMR des isotopes 11 B et 27 Al n'appuient donc pas la présence de B ou Al en coordinence tétraédrique au delà du seuil de détection dans ces échantillons. Ces résultats concordent avec nos affinement reposant sur des facteurs de dispersion, ionisé dans le cas de O et pour un atome neutre dans le cas de Si, ce qui laisse croire que ce choix de courbes produit des résultats plus justes qu'un affinement avec seulement des facteurs pour atomes neutres. Les distances tombent dans l'intervalle 1.904-1.907 Å, avec une moyenne globale de 1.9047(8) Å, et l'affinement des structures indique des valeurs de dispersion aux sites en accord avec une occupation complète du site Z par Al. C'est donc dire que dans ce cristal zoné de façon complexe, Si est égal à 6.00 apfu, ainsi que Z Al. (Traduit par la Rédaction) Mots-clés: liddicoatite, elbaïte, tourmaline, zonation oscillatoire, affinement de la structure cristalline, analyse avec une micro-sonde électronique, résonance magnétique nucléaire avec spin à l'angle magique, spectroscopie de Mössbauer, populations des sites, Anjanabonoina, Madagascar.
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It is now well known that Si, B and OH + F are variable components of tourmaline, and yet the stereochemical details of their variation in the tourmaline structure are still not well characterized or understood. Application of the valence-sum rule of bond-valence theory to questions of short-range atomic arrangements shows that there are considerable stereochemical constraints associated with the variation of Si, B and OH + F in the tourmaline structure. The occurrence of a trivalent cation (Al, B) at the T site must be locally associated with the occurrence of trivalent cations (Al, Fe3+) at the neighboring Y and Z sites, and possibly with Ca at the neighboring X site. In Li-free tourmaline, the occurrence of O2- at O(1) (i.e., OH + F < 4 apfu) must be locally associated with 3Al or 2Al + Mg (or the Fe2+-Fe3+ analogues) at the adjacent 3Y sites in order for the valence-sum rule to be satisfied on a local scale. In Li-bearing Mg-free tourmaline, O2- at O(1) must be locally associated with 3Al at the adjacent 3Y sites. These requirements provide stringent constraints on the possible substitution schemes whereby additional O2- (i.e, a deficiency in OH + F) is incorporated into tourmaline.
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ABSTRACI Thestructuresof ninegem-qualitycrystalsof V-bearing vite,a=15.95,c=7.17 A y= 1530 43,R3*,havebeenrefined to R indices of. -227o using graphite-monochromated MoKcl X-radiation; the crystals used for the X-ray dala collection were analyzed using an electron microprobe. The Si content of these crystals is significantly less than 6 atoms per formula unit; zrssignment of talAl sufficient to fill the Ji site results in a linear relationship between and t4lAI content. Examination of recent results of stucture refinement for tourmalile shows no well-defined relationship between 44> and constituent Lczf;:on radius. Conversely, there is a well-developed linear relationship between and constifirent l-cation radius. Site-scattering refinement shows F to be strongly to completely ordered at the O(1) site. There is no significant positional disorder at the O(1) or O(2) sites.
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Yellow-brown to pink Mn-rich tourmalines with MnO contents in the range 8-9 wt% MnO (∼0.1 wt% FeO) from a recently discovered locality in Austria, near Eibenstein an der Thaya (Lower Austria), have been characterized by crystal structure determination, by chemical analyses (EMPA, SIMS), and by optical absorption spectroscopy. Qualitatively, the optical spectra show that Mn2+ is present in all regions of the crystals, and that there is more Mn3+ in the pink regions (∼8% of the total Mn is Mn3+) than in the yellow-brown regions. A gamma-ray irradiated crystal fragment is distinctly pink compared to the yellow-brown color of the sample before irradiation, but it still has hints of the yellow-brown color, which suggests that the natural pink color in Mn-rich tourmaline from this locality is due to natural irradiation of the initial Mn2+. For these Mn-rich and Li-bearing olenite samples, crystal structure refinements in combination with the chemical analyses give the optimized formulae X(Na0.80Ca0.01□0.19) T(Si5.80Al0.20) B3O27 [(OH)3.25F0.43O0.32], with a = 15.9466(3) Å, c = 7.1384(3) Å, and R = 0.036 for the sample with ∼9 wt% MnO, and X(Na0.77Ca0.03□0.20) Y(Al1.23Mn1.142+Li0.48Fe0.022+Ti0.01□0.12) ZAl6T(Si5.83Al0.17 ) B3O27 [(OH)3.33F0.48O0.19] for a sample with a = 15.941(1) Å, c = 7.136(1) Å, R = 0.025 and -8 wt% MnO. The refinements show 1.22-1.25 Al at the Y site. As the Mn content increases, the Li and the F contents decrease. The Li content (0.37-0.48 apfu) is similar to, or lower than, the Li content of olenite (rim-composition) from the type locality, but these Mn-rich tourmalines do not contain [4]B. Like the tourmaline from Eibenstein an der Thaya, synthetic Mn-rich tourmaline (in a Li + Mn-bearing system), containing up to ∼0.9 apfu Mn (∼6.4 wt% MnO), is aluminous but not Li-rich. This study demonstrates that although a positive correlation exists between Mn and Li (elbaite) in tourmaline samples from some localities, this coupling is not required to promote compatibility of Mn in tourmaline. The a parameter in Mn-rich tourmalines (MnO: ≥3 wt%) is largely a function of the cation occupancy of the Y site (r2 = 0.97).
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Tourmaline has recently been shown to incorporate large amounts of substituent B at the tetrahedral site. To characterize the response of the tourmaline atomic arrangement to differing amounts of substitution of B for Si, five samples were separated from a core-to-rim (-3 mm) section of an Fe-bearing olenite with a dark green core and a nearly colorless rim from Koralpe, Austria. Crystal structures of the five samples were refined to R values <0.018 using three-dimensional X-ray methods, and the compositions of the crystals were determined by electron microprobe, secondary ion mass spectrometric, and Mössbauer analyses. From core to rim. [4]B increases monotonically from 0.35 to 0.65 apfu, whereas the mean T-O distance decreases from 1.621 to 1.610 Å. Optimized formulae using chemical and structural data range from X(Na0.632Ca0.145□0.223) 0.150) ZAl6.00 B3.00T(Si5.525B0.333Al0.130 Be0.012)O27[(OH)3.19O0.81] (core composition) to X(Na0.408Ca0.290 K0.002□0.300) Y(Al2.338 Li0.365Fe2+0.084Mn2+0.009Mg0.005Ti0.005□0.194) ZAl6.00 B3.00T (Si4.989B0.615Al0.362Be0.034) O27 [(OH)3.41O0.59] (rim composition). The variation of chemistry and structure, coupled with short-range order constraints, demonstrates that (I) the average tetrahedral bond length ( ) reflects the substitution of 141B, (2) tourmaline samples with relatively high Fe2+ contents (ca. 1 apfu Fe2+) and distances up to 1.621 Å can contain significant amounts of [4]B (up to ca. 0.3 apfu), (3) the presence of substantial [4]B is limited to, or more common in Al-rich tourmalines, (4) the presence of [4]B substituents favors OH at the O3 site, (5) the presence of Ca or Na at the X site is not simply correlated with occupancy of [4]B in the adjacent tetrahedral ring, and (6) no two B-substituted tetrahedra will link through bridging O atoms.
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Twelve tourmaline specimens spanning the entire range of Fe - Mg substitution were analyzed by electron microprobe and crystal-structure refinement to determine partitioning of these elements into the 2 octahedral sites, Y and Z. For each specimen the empirical formula, cell parameters, atomic coordinates, mean bond lengths, atomic site occupancies and bond-valence sums are given. Disorder of Mg between the Y and Z sites of the tourmaline structure is relatively common for many compositions and significantly complicates formula calculation. To enable formula calculation in the absence of detailed structural information, structural-compositional correlations were sought. A good correlation exists between the partitioning behaviour of Mg and total Fe/(Fe+Mg), i.e. Mg(Y) = 3 [1 - Fe/(Fe+Mg)], but the Y-site Mg content can only be reliably calculated with this equation for compositions with FeO(total) greater than 7 wt.%; However, the Mg content at the Z site (and by deduction, at the Y site) can be calculated for all compositions from the chemical composition and unit cell volume (V) by: Z[Mg/(Mg+Al)] = 0.0209(exp[(V-1540)/40] - 1]. The substitutions of Ti4+ and B for Si and of OH and F for O are discussed. The method of calculation for the correct empirical formula of a tourmaline is given.
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Considerable uncertainty has surrounded the occurrence of tetrahedrally coordinated Al and B at the T site in tourmaline. Although previously detected in several tourmaline specimens, the frequency of these substitutions in nature, as well as the extent to which they occur in the tourmaline structure, is not known. Using 11B and 27Al MAS NMR spectroscopy, we have investigated the presence of B and Al at the T site in 50 inclusion-free tourmaline specimens of low transition-metal content and different species (elbaite, “fluorelbaite,” liddicoatite, dravite, uvite, olenite, and magnesiofoitite) from different localities worldwide. Chemical shifts of [4]B and [3]B in 11B spectra, and [4]Al and [6]Al in 27Al spectra, are well resolved, allowing detection of even small amounts of T-site constituents. In the observed spectra, [4]B and [3]B peaks are located at 0 and 18–20 ppm, respectively, with the greatest intensity corresponding to [3]B (=3 apfu). In 27Al spectra, [4]Al and [6]Al bands are located at 68–72 and 0 ppm, respectively, with the greater intensity corresponding to [6]Al. However, inadequate separation of YAl and ZAl precludes resolution of these two bands. Simulation of 11B MAS NMR spectra shows that tetrahedrally and trigonally coordinated B can be readily distinguished at 14.1 T and that a [4]B content of 0.0–0.5 apfu is common in tourmaline containing low amounts of paramagnetic species. 27Al MAS NMR spectra show that Al is also a common constituent of the T site in tourmaline. Determination of [4]Al content by peak-area integration commonly shows values of 0.0–0.5 apfu. Furthermore, the chemical shift of the 27Al tetrahedral peak is sensitive to local order at the adjacent Y and Z octahedra, where [4]Al-YMg3 and [4]Al-Y(Al,Li)3 arrangements result in peaks located at ~65 and ~75 ppm, respectively. Both 11B MAS NMR and 27Al MAS NMR spectra show peak broadening as a function of transition-metal content (i.e., Mn2+ + Fe2+ = 0.01–0.30 apfu) in the host tourmaline. In 11B spectra, broadening and loss of intensity of the [3]B signal ultimately obscures the signal corresponding to [4]B, increasing the limit of detection of [4]B in tourmaline. Our results clearly show that all combinations of Si, Al, and B: T = (Al, Si)6, T = (B, Si)6, T = (Al, B, Si)6, and T = Si6 apfu, are common in natural tourmalines.
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Crystal structure refinement of copper-bearing tourmaline from Paraiba, Brazil, rim composition {Na0.54Ca0.05}{Li1.21Mn0.04Cu0.10Al1.66}Al-6{Si5.92Al0.08}O-18{BO3}(3){(OH)(3.56)F-0.44}, core composition {Na0.55Ca0.01}{Li1.16Mn0.08Cu0.05Al1.71}Al-6{Si5.88Al0.12}O-18{BO3}(3){(OH)(3.70)F-0.30}, shows the octahedrally coordinated Z site to be completely occupied by Al, and Li to occur only at the octahedrally coordinated Y site. The high displacement factors at the O1 and O2 positions indicate significant positional disorder that is induced by occupancy of the X [similar or equal to 0.57 Na + 0.43 square (vacancy)] and Y [similar or equal to 1.2 Li + 1.8(Al + Mn3+)] sites by cations of very different size and charge.
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We report here the results of a series of inclusive chemical characterizations, including all elements except oxygen, for a suite of 54 tourmaline samples. A combination of analytical techniques was used to analyze for major and light elements (electron microprobe), Fe 31 (Mossbauer spectroscopy), H (U extraction), and B, Li, and F (ion microprobe, or SIMS). The B content of the tourmalines studied ranges from 2.86 to 3.26 B per formula unit (pfu) with 31 anions; excess boron is believed to reside in the Si site. Li ranges from 0.0 to 1.44 Li pfu and F contents are 0.0-0.91 pfu. H contents range from nearly anhydrous up to 3.76 H pfu and do not correlate simply with Fe 31 content. Mossbauer results show that tourmaline exhibits the entire range of Fe 31 /SFe from 0.0-1.0. Fe 21 is represented in the spectra by three doublets, with occupancy in at least three distinct types of Y sites (with different types of nearest and next nearest neighbors). Fe 31 was found in 26 of the 54 samples studied. Although Mossbauer data do not allow the distinction between (Y) Fe 31 and (Z) Fe 31 site occupancies to be made, XRD data on these samples suggest that the majority of Fe 31 is also in Y. Of the samples studied, (4) Fe 31 occurs in nine; five of those were either olenite or uvite with extensive Na substitution. A mixed valence doublet corresponding to delocalized electrons shared between adjacent octahedra was observed in 14 of the samples studied. Projection pursuit regression analysis shows that distribution of Fe among doublets is a function (albeit a complex one) of bulk composition of the tourmaline and supports the interpretation of doublets representing different populations of neighbors. Variations in Fe 31 /
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Chemical analyses of tourmaline crystals from a small pegmatite body, nearby the Sto¡htte, Koralpe (Styria, Austria), exhibit a pronounced excess in boron, expressed by the simpli¢ed formula (Na0.43 Ca0.24&0:33) (Al2.43Li0.33&0:28)Al6(BO3)3(B1.23 Si4.87 O18)(O0.64(OH)3.36). A substantial substitution of silicon by boron in the tetrahedral position is in agree- ment with an occupation re¢nement in single crystal X-ray work: the average (Si, B)-O bond length measures1.610—.This is the ¢rst example forasubstitutionofsiliconbyboroninanaturaltourmaline,thatcouldbe veri¢ed bycrystallographic methods.
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The crystal structure of a dravite (tourmaline) sample from Osarara, Narok District, Kenya, a = 15.947(2), c = 7.214(1) angstrom, V = 1589.0(6) angstrom3, R3m, has been refined to an R index of 2.0% based on 1136 reflections measured with MoKalpha X-radiation. Electron microprobe analysis, site-scattering refinement, electronic absorption (published), stereochemical analysis, and Mossbauer spectra show the structural formula to be x(Na0.814-Ca0.009K0.014square0.163)y(Mg1.301Mn0.003Fe0.0512+Fe0.5603+3Cr0.006Ti0.030Al0.985)z(Al5.090Mg0.910)(BO3)3Si6O18-(O,OH)4. Of particular interest is the assignment of significant Mg to the Z site and Al to the Y site. For published structural refinements of tourmaline, the grand mean size of the Y and Z polyhedra is a linear function of the constituent cation radii. That is not the case for the Y and Z sites individually. However, greatly improved linearity occurs if significant Mg is assigned to the Z site for some compositions when Al > 6.0 atoms pfu; this indicates that the usual assumption that Al completely occupies the Z site before occupying any other site is not universally correct.
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The structures of eight crystals of manganiferous elbaite, a almost-equal-to 15.90, c = 7.12 angstrom, V almost-equal-to 1560 angstrom3, R3m, have been refined to R indices of approximately 2.2% using graphite-monochromated MoKalpha X-radiation; the crystals used for the X-ray data collection were analyzed using an electron microprobe. We obtain very close agreement between Li contents estimated from stoichiometric constraints and the results of electron-microprobe analyses, and Li contents calculated from the site-scattering refinements, suggesting that both methods give accurate Li contents for elbaite (where the correct valence state of the transition metals are known). A previously developed relationship between [Y-O] and constituent-cation radius shows both Mn and Fe to be completely in the divalent state in these crystals. They all show very strong positional disorder of the 01 and 02 anions. This is also a common (although not ubiquitous) feature of many refinements of tourmaline reported in the literature, and may be quantitatively interpreted in terms of local disorder induced by occupancy of the Y site by cations of very different size and charge.
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The crystal structures of 23 samples extracted from a large slice oriented along (001) of a single crystal of liddicoatite from the Anjanabonoina granitic pegmatite in Madagascar (showing pronounced, visually discontinuous oscillatory zones and anomalous biaxiality) were refined to R1 indices of 1.5-2.9% (< R-1 > = 1.78%). Cell parameters are in the range a approximate to 15.82-15.87, c approximate to 7.10-7.12 angstrom. Spindle-stage measurement of 2V gave values of 0.0 degrees for a fragment from the (001) zone and 8(3) and 18.9(5) for fragments from the pyramidal zone of the crystal. However, single-crystal X-ray intensity data show no deviation from 3m Laue symmetry, indicating that there is no information in the diffraction data on any deviation from R3m symmetry. The < T-O > distances are in the range 1.616-1.619 angstrom, with a grand mean value of 1.6175(7) angstrom. The occupancy of the T site was expressed as xSi + (1-x) B, and x was treated as variable in the refinement procedure. The effect of using different scattering factors (i.e., ionized versus neutral) on the refined site-occupancies was investigated in detail. The grand mean refined [4] B content of the T site varies from -0.04 apfu for ionized scattering-curves for O and Si to 0.25 apfu for neutral scattering-curves for O and Si, illustrating the effect of the use of different scattering curves on refined [4] B site-populations. Examination of < T-O > distances as a function of aggregate cation radius for tourmalines containing ([4]) B and Al-[4] shows a large amount of scatter, emphasizing the need for more accurate data. The limits of detection for B-11 and Al-27 in tourmaline by Magic-Angle-Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy were investigated by simulation. For minimum (< 0.04 apfu) and maximum (0.12 apfu) contents of (paramagnetic) transition metals, the limits of detection of B-[4] are similar to 0.02 and 0.08 apfu, and of ([4]) Al are similar to 0.01 and 0.01 apfu, respectively. B-11 and Al-27 MAS NMR spectroscopy gave no evidence of the presence of tetrahedrally coordinated B or Al at the T site above these detection limits in any sample. This result is in accord with our refinement results using an ionized scattering-curve for O and a neutral scattering-curve for Si, suggesting that use of these curves is giving more accurate results than refinement with neutral scattering factors. The < Z-O > distances are in the range 1.904-1.907 angstrom, with a grand mean value of 1.9047(8) angstrom, and structure refinement indicates site-scattering values in accord with complete occupancy of the Z site by Al. Hence throughout this complexly zoned crystal, Si = 6.00 apfu and Al-Z = 6.00 apfu.
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A nomenclature for tourmaline-supergroup minerals is based on chemical systematics using the generalized tourmaline structural formula: XY(3)Z(6)(T(6)O(18))(BO(3))(3)V(3)W, where the most common ions (or vacancy) at each site are X = Na(1+), Ca(2+), K(1+), and vacancy; Y = Fe(2+), Mg(2+), Mn(2+), Al(3+), Li(1+), Fe(3+), and Cr(3+); Z = Al(3+), Fe(3+), Mg(2+), and Cr(3+); T = Si(4+), Al(3+), and B(3+); B = B(3+); V = OH(1-) and O(2-); and W = OH(1-), F(1-), and O(2-). Most compositional variability occurs at the X, Y, Z, W, and V sites. Tourmaline species are defined in accordance with the dominant-valency rule such that in a relevant site the dominant ion of the dominant valence state is used for the basis of nomenclature. Tourmaline can be divided into several groups and subgroups. The primary groups are based on occupancy of the X site, which yields alkali, calcic, or X-vacant groups. Because each of these groups involves cations (or vacancy) with a different charge, coupled substitutions are required to relate the compositions of the groups. Within each group, there are several subgroups related by heterovalent coupled substitutions. If there is more than one tourmaline species within a subgroup, they are related by homovalent substitutions. Additionally, the following considerations are made. (1) In tourmaline-supergroup minerals dominated by either OH(1-) or F(1-) at the W site, the OH(1-)dominant species is considered the reference root composition for that root name: e.g., dravite. (2) For a tourmaline composition that has most of the chemical characteristics of a root composition, but is dominated by other cations or anions at one or more sites, the mineral species is designated by the root name plus prefix modifiers, e.g., fluor-dravite. (3) If there are multiple prefixes, they should be arranged in the order occurring in the structural formula, e.g., "potassium-fluor-dravite."
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A systematic classification of the tourmaline-group minerals, general formula X Y-3 Z(6) (T6O18) (BO3)(3) V3W, is proposed, based on chemical composition and ordering at the different crystallographic sites of the tourmaline structure. There are currently thirteen accepted tourmaline species. However, based on the actual chemical compositions of holotype material, several of these species were imprecisely or incorrectly defined. X proper definition of these species is proposed. A crystal-chemical feature that extends the number of possible end-members is the anion occupancy of the W-site (dominated by OH-, F- or O2-) and the V-site (dominated by OH- or, more rarely, O2-). Thus, based on the W-site alone, there can be hydroxy-, fluor-, or oxy-end-members. Furthermore, the presence of dominant O2- at the Iii-site commonly requires local cation-ordering at the Y- and Z-sites. The tourmaline-group minerals can be divided into three principal groups based on the dominant species at the X-site: alkali tourmalines (Nn), calcic tourmalines (Ca) and X-site-vacant tourmalines (square: vacancy). These groups are further divided, initially based on the W-site occupancy, then by the (actual or inferred) V-sire occupancy, next by the (actual or inferred) Y-site occupancy and, finally, by the (actual or inferred) Z-site occupancy. A systematic classification procedure is developed that takes into account different levels of knowledge of the chemical composition and site occupancy of the tourmaline. Several examples are used to illustrate the application of this classification procedure.
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Fe^(2+)- and Mn^(2+)-rich tourmalines were used to test whether Fe^(2+) and Mn^(2+) substitute on the Z site of tourmaline to a detectable degree. Fe-rich tourmaline from a pegmatite from Lower Austria was characterized by crystal-structure refinement, chemical analyses, and Mössbauer and optical spectroscopy. The sample has large amounts of Fe^(2+) (~2.3 apfu), and substantial amounts of Fe^(3+) (~1.0 apfu). On basis of the collected data, the structural refinement and the spectroscopic data, an initial formula was determined by assigning the entire amount of Fe^(3+) (no delocalized electrons) and Ti^(4+) to the Z site and the amount of Fe^(2+) and Fe^(3+) from delocalized electrons to the Y-Z ED doublet (delocalized electrons between Y-Z and Y-Y): X(Na_(0.9)Ca_(0.1)) ^Y(Fe^(2+)_(2.0)Al_(0.4)Mn^(2+)_(0.3)Fe^(3+)_(0.2)) ^Z(Al_(4.8)Fe^(3+)_(0.8)Fe^(2+)_(0.2)Ti^(4+)_(0.1)) ^T(Si_(5.9)Al_(0.1))O_(18) (BO_3)_3^V(OH)_3 ^W[O_(0.5)F_(0.3)(OH)_(0.2)] with α = 16.039(1) and c = 7.254(1) Å. This formula is consistent with lack of Fe^(2+) at the Z site, apart from that occupancy connected with delocalization of a hopping electron. The formula was further modified by considering two ED doublets to yield: ^X(Na_(0.9)Ca_(0.1)) ^Y(Fe^(2+)_(1.8)Al_(0.5)Mn^(2+)_(0.3)Fe^(3+)_(0.3)) ^Z(Al_(4.8)Fe^(3+)_(0.7)Fe^(2+)_(0.4)Ti^(4+)_(0.1)) ^T(Si_(5.9_Al_(0.1))O_(18) (BO_3)_3 ^V(OH)_3 ^W[O_(0.5)F_(0.3)(OH)_(0.2)]. This formula requires some Fe^(2+) (~0.3 apfu) at the Z site, apart from that connected with delocalization of a hopping electron. Optical spectra were recorded from this sample as well as from two other Fe^(2+)-rich tourmalines to determine if there is any evidence for Fe^(2+) at Y and Z sites. If Fe^(2+) were to occupy two different 6-coordinated sites in significant amounts and if these polyhedra have different geometries or metal-oxygen distances, bands from each site should be observed. However, even in high-quality spectra we see no evidence for such a doubling of the bands. We conclude that there is no ultimate proof for Fe^(2+) at the Z site, apart from that occupancy connected with delocalization of hopping electrons involving Fe cations at the Y and Z sites. A very Mn-rich tourmaline from a pegmatite on Elba Island, Italy, was characterized by crystal-structure determination, chemical analyses, and optical spectroscopy. The optimized structural formula is ^X(Na_(0.6)□_(0.4)) ^Y(Mn^(2+)_(1.3)Al_(1.2)Li_(0.5)) ^ZAl_6 ^TSi_6O_(18) (BO_3)_3 ^V(OH)_3 ^W[F_(0.5)O_(0.5)], with α = 15.951(2) and c = 7.138(1) Å. Within a 3σ error there is no evidence for Mn occupancy at the Z site by refinement of Al ↔ Mn, and, thus, no final proof for Mn^(2+) at the Z site, either. Oxidation of these tourmalines at 700–750 °C and 1 bar for 10–72 h converted Fe^(2+) to Fe^(3+) and Mn^(2+) to Mn^(3+) with concomitant exchange with Al of the Z site. The refined ^ZFe content in the Fe-rich tourmaline increased by ~40% relative to its initial occupancy. The refined YFe content was smaller and the distance was significantly reduced relative to the unoxidized sample. A similar effect was observed for the oxidized Mn^(2+)-rich tourmaline. Simultaneously, H and F were expelled from both samples as indicated by structural refinements, and H expulsion was indicated by infrared spectroscopy. The final species after oxidizing the Fe^(2+)-rich tourmaline is buergerite. Its color had changed from blackish to brown-red. After oxidizing the Mn^(2+)-rich tourmaline, the previously dark yellow sample was very dark brown-red, as expected for the oxidation of Mn^(2+) to Mn^(3+). The unit-cell parameter α decreased during oxidation whereas the c parameter showed a slight increase.
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The quantitative determination of light element concentrations in geological specimens represents a major analytical challenge as the electron probe is generally not suited to this task. With the development of new in situ analytical techniques, and in particular the increasing use of secondary ion mass spectrometry, the routine determination of Li, Be and B contents has become a realistic goal. However, a major obstacle to the development of this research field is the critical dependence of SIMS on the availability of well characterized, homogeneous reference materials that are closely matched in matrix (composition and structure) to the sample being studied. Here we report the first results from a suite of large, gem crystals which cover a broad spectrum of minerals in which light elements are major constituents. We have characterized these materials using both in situ and wet chemical techniques. The samples described here are intended for distribution to geochemical laboratories active in the study of light elements. Further work is needed before reference values for these materials can be finalized, but the availability of this suite of materials represents a major step toward the routine analysis of the light element contents of geological specimens. light elements, tourmaline, danburite, spodumene, muscovite, isotopes. Copyright © Association Scientifique pour la Gŕologie et ses Applications.
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Distortion parameters [, 2 , DI(Y–O), DI(O–Y–O), DI(O–O)] have been calculated for cation polyhedra in tourmalines of different chemical compositions. Tourmalines with greater amounts of small, highly charged ions in the YO 6 octahedron display greater bond-length distortion in Y. The size and charge of the occupants at the Y site have been included in an empirically determined formula intended to evaluate the bond-length distortion of the YO 6 octahedron. This equation demonstrates that the bond-length distortion in the YO 6 octahedron is a function of the size and charge of the Y-site occupants, and is predictable from those occupants (r = 0.972 for observed versus calculated distortion). The distortion of the Z octahedron in a tourmaline is largely a function of the <Y–O> of that tourmaline [r = –0.985 for all tourmalines where O3 is occupied by 3 (OH) apfu], although the occupant of the O3 site also affects that distortion. The bond-length distortion of the TO 4 tetrahedron is small, but examination of the angle distortion of the tetrahedron demonstrates a strong covariance with the charge at the X site (r = 0.892). Finally, distortions in the XO 9 polyhedron were found to correlate with the charge of the occupants at the Y site and the fluorine content (r = 0.881).
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The substitution of [4] B for [4] Si in tourmaline has been the source of much discussion. A sample of olenite from Stoffhütte, Koralpe, Styria, Austria has been found to contain more than one [4] B per formula unit of 31 (O,OH,F), demonstrating that significant [4] B = [4] Si substitution does indeed occur in tourmaline. The composition of the structurally characterized crystal was determined using electron microprobe and SIMS data; in combination with refinement of the site scattering, the chemical data yield an optimized formula of Y (Na 0.400 Ca 0.294 0.306) Z (Al 2.424 Li 0.357 0.219) (Al 5.916 0.084) B 3.00 (Si 4.854 B 1.062 Al 0.084) 6.00 O 27 [F 0.06 (OH) 3.31 O 0.63 ]. The Austrian olenite crystallizes in space group R3m, a 15.731(3), c 7.0638(9) Å. The atomic arrangement was refined to R = 0.014 using X-ray data; <T–O> is equal to 1.609 Å, reflecting substitution of the smaller boron atom for Si. Conjecture on the pattern of distribution of [4] B can be made on the basis of X-site occupancy.
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The crystal structure of the Na-(Al, Mn, Li)-tourmaline tsilaisite was refined to a R-value of 2.9%. The structure is closely related to the crystal structures of elbaite and schorl, and manganese was found to occupy exclusively Y sites in the tsilaisite structure. (Authors' abstract)-E.v.P.
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Alkali-deficient schorl, (Na0.55□0.45)(Fe2+1.76Al0.89Mg0.33-Ti0.02)Al6 (BO3)3(Si5.86Al0.14)O18.48((OH)3.38F0.14), is rhombohedral with a = 15.963(3) and c = 7.148(2) Å; its space group is R3m. The 3a alkali site in the alkali-deficient schorl with an occupancy of (Na0.55□0.45) is the largest yet observed in tourmaline. Substitution of cations smaller than Na, notably Ca, affects the configuration of the six-membered tetrahedral ring by decreasing its degree of "crimping' and by increasing its ditrigonality and the distortion of its tetrahedra. The only observed effect of Al → Si substitution is an increase in the size of the tetrahedra. R2+ → R3+ substitution in the 9b octahedral site in response to the dehydroxylation-type substitution, (OH)- + R2+ = O2 + R3+, and alkali defect-type substitution, R+ + R2+ = 3a□ + R3+, results in increased "puckering' and in a marked compression of the smaller 18c octahedra with which the larger 9b octahedra share edges. The volume of the unit cell is highly correlated to the weighted-mean size of the 9b and 18c octahedra. -from Author
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Pink, Mn-bearing “oxy-rossmanite” from a pegmatite in a quarry near Eibenstein an der Thaya, Lower Austria, has been characterized by crystal structure determination, chemical analyses (EMPA, SIMS), and optical absorption and infrared spectroscopy. Crystal structure refinements in combination with the chemical analyses give the optimized formulae ^X(□ _(0.53)Na_(0.46)Ca_(0.01))Y^(Al_(2.37)Li_(0.33)Mn^(2+)_(0.25)Fe^(2+)_(0.04)Ti^(4+)_(0.01))^ZAl_6^T(Si_(5.47)Al_(0.28)B_(0.25))O_(18)(BO_3)_3^V[(OH)_(2.85)O_(0.15)] ^W[O_(0.86)(OH)_(0.10)F_(0.04)], with ɑ = 15.8031(3), c = 7.0877(3) Å, and R = 0.017 for the sample with 2.05 wt% MnO, and ^X(□_(0.53)Na_(0.46)Ca_(0.01))^Y (Al_(2.35)Li_(0.32)Mn^(2+)_(0.28)Fe^(2+)_(0.04)Ti^(4+)_(0.01))^ZAl_6^T(Si_(5.51)Al_(0.25)B_(0.24))O_(18)(BO_3)_3 ^V[(OH)_(2.80)O_(0.20)]^W[O_(0.86)(OH)_(0.10)F_(0.04)] for a sample with ɑ = 15.8171(3), c = 7.0935(2) Å, R = 0.017, and 2.19 wt% MnO. Although the structure refinements show significant amounts of ^([4])B, the bond-lengths (~1.620 Å) mask the incorporation of ^([4])B because of the incorporation of ^([4])Al. The distances, calculated using the optimized T site occupancies, are consistent with the measured distances. This “oxy-rossmanite” shows that it is possible to have significant amounts of ^([4])B and ^([4])Al in an Al-rich tourmaline. The “oxy-rossmanite” from Eibenstein has the highest known Al content of all natural tourmalines (~47 wt% Al_2O_3; ~8.6 apfu Al). The near-infrared spectrum confirms both that hydroxyl groups are present in the Eibenstein tourmaline and that they are present at a lower concentration than commonly found in other lithian tourmalines. The integrated intensity (850 cm^(−2)) of the OH bands in the single-crystal spectrum of “oxy-rossmanite” from Eibenstein is distinctly lower than for other Li-bearing tourmaline samples (970–1260 cm^(−2)) with OH contents >3.0 pfu. These samples fall on the V site = 3 (OH) line in the figure defining covariance of the relationship between the bond-angle distortion (σ_(oct)^2) of the ZO_6 octahedron and the distance. On a bond-angle distortion- distance diagram “oxy-rossmanite” from Eibenstein lies between the tourmalines that contain 3 (OH) at the V site, and natural buergerite, which contains 0.3 (OH) and 2.7 O at the V site. No H could be found at the O1 site by refinement, and the spherical electron density in the difference-Fourier map around the O1 site supports the conclusion that this site is mainly occupied by O. The pink color comes from the band at 555 nm that is associated with Mn^(3+) produced by natural irradiation of Mn^(2+). This is the first time a tourmaline is described that has a composition that falls in the field of the previously proposed hypothetical species “oxy-rossmanite”.
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Gem-quality elbaite from Paraíba, Brazil, containing up to 1.4 wt% Cu has been characterized using optical spectroscopy and crystal chemistry. The optical absorption spectra of Cu^(2+) in these tourmalines consist of two bands with maxima in the 695- to 940-nm region that are more intense in the E ⊥ c direction. The vivid yellowish green to bluegreen colors of these elbaite samples arise primarily from Cu^(2+) and are modified to violetblue and violet hues by increasing absorptions from Mn^(3+).
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Unusually vivid tourmalines from the state of Paraíba, in northeastern Brazil, have attracted great interest since they first appeared on the international gem market in 1989. This article describes what is known of the locality at this time, but focuses on the most striking characteristic of these gem tourmalines: the unusual colors in which they occur. Quantitative chemical analyses revealed that these elbaite tourmalines contain surprisingly high concentrations of copper, up to 1.92 wt.% Cu (or 2.38 wt.% CuO). Their colors are due to Cu^(2+) or a combination of Cu^(2+), Mn^(3+), and other causes. Some colors can be produced by heat treatment, but most also occur naturally.
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Significant amounts of boron in both trigonal and tetrahedral coordination have been found through 11B magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy of natural olenite (aluminum-rich tourmaline) from Stoffhütte, Koralpe, Styria, Austria. The 11B MAS NMR spectrum consists of a superposition of two quadrupolar MAS peaks. A broad peak with δiso = 18.3 ppm, νQ = 1410 KHz, and η = 0.11 demonstrates the trigonal-planar environment of the BO3 group (relative area ratio = 80%). The narrow symmetrical peak (δiso = 0.0 ppm, νQ = 300 KHz, η = 0.00) represents tetrahedral BO4 groups (relative area ratio = 20%). An infrared spectrum shows hydroxyl stretching bands at low wavenumbers indicating that underbonded O atoms of the hexagonal ring (due to a partial replacement of [4]Si4+ by [4]B3+) form relatively strong hydrogen bonds with the protons of the hydroxyl groups. A 29Si MAS NMR spectrum shows a peak consisting of a main signal at −90 ppm and a shoulder at about −85 ppm. The main signal originates from Si atoms connected (via oxygen bridges) to two other Si atoms in the hexagonal ring, and the minor signal is from Si atoms connected to one Si and one B atom. No signal corresponding to [6]Si was detected in this natural olenite sample.
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Tsilaisite, NaMn 3Al 6(Si 6O 18)(BO 3) 3(OH) 3OH, is a long-expected new mineral of the tourmaline supergroup. It occurs in an aplitic dike of a LCT-type pegmatite body from Grotta d'Oggi, San Pietro in Campo, island of Elba, Italy, in association with quartz, K-feldspar, plagioclase, elbaite, and schorl. Crystals are greenish yellow with a vitreous luster, a white streak, and show no fluorescence. Tsilaisite has a Mohs hardness of approximately 7; it is brittle with a sub-conchoidal fracture, and has a calculated density of 3.133 g/cm 3. In plane-polarized light, tsilaisite is pleochroic, O = pale greenish yellow, E = very pale greenish yellow; it is uniaxial negative, ω = 1.645(5), ε = 1.625(5). Tsilaisite is rhombohedral, space group R3m, a = 15.9461(5), c = 7.1380(3) Å, V = 1571.9(1) Å 3, Z = 3. The strongest eight X-ray-diffraction lines in the powder pattern [d in Å(I)(hkl)] are: 3.974(100)(220), 2.942(94)(122), 2.570(79)(051), 2.034(49)(152), 4.205(41)(211), 6.329(22)(101), 2.377(21)(003), and 1.592(21)(550). Analysis by a combination of electron microprobe, secondary ion mass spectrometry, and optical absorption spectroscopy gives SiO 2 = 36.10(3), TiO 2 = 0.32(4), Al 2O 3 = 37.10(5), MnO = 9.60(10), CaO = 0.09(4), Na 2O = 2.11(7), K 2O = 0.03(1), F = 0.79(3), B 2O 3 = 10.2(6), Li 2O = 0.8(1), H 2O = 3.1(2), sum 99.95 wt%. The unit formula is X(Na 0.670.30Ca 0.02K 0.01) Y(Mn 2+ 1.34Al 1.14Li 0.54Ti 0.04) ZAl 6 T(Si 5.94Al 0.06)B 2.91O 27 V(OH) 3 W(OH 0.39F 0.41O 0.20). The structure, refined also taking into account the positional disorder of the O1 and O2 anions, converged to statistical indices R1 for all reflections of about 2%. The resulting site populations indicate that the Z site is occupied by Al and that the Y site is dominated by Mn 2+. Aluminum is incorporated at Y through two types of substitutions: YAl+ WO 2- → YMn 2++ WOH, which has the result of replacing OH at the W site by O 2-, and Y(Al+Li)+ WF → 2 YMn 2++ WOH, which relates fluor-elbaite to the tsilaisite component. Infrared absorption spectra measured in the principal OH-stretching region were interpreted on the basis of local arrangements consistent with the short-range bond-valence requirements. A compositional trend from fluor-elbaite to tsilaisite is observed in samples from Elba Island. The occurrence of tsilaisite is very rare in nature, as a consequence of both the requirement of extraordinary petrogenetic conditions and limited structural stability.
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The crystal chemistry of seven crystal fragments taken from differing regions of the same colorless to yellow-greenish tourmaline macro-crystal from pegmatite pockets in aplite veins (island of Elba, Italy) was studied with a multi-disciplinary (SREF, XRDT) and multi-analytical approach (EMPA, SIMS). EMPA and XRDT studies showed relationships between color and chemical zoning and crystal-growth evolution, indicating which fragments could be considered representative of the chemical evolution of the genetic micro-environment in which the crystal developed. Results showed that the colorless fragment is an elbaite while the yellow-greenish crystal fragments are Mn2+-rich (up to 1.34 apfu) and belong to the alkali group and fluor subgroup. They are characterized by dehydroxylation and alkali-defect type substitutions that cooperate in reducing Li and increasing Mn contents. The Y site is populated by Al, Li, and Mn2+, and the Z site by Al and Mn2+ (up to 0.10 apfu). In contrast with data in the literature, Mn2+ populates both octahedral sites according to the order-disorder reaction: YMn + ZAl ↔ YAl + ZMn. As Mn2+ content increases, progressive disorder takes place. This disorder is quantitatively lower than that of the ZMg in dravite, due to the low structural tolerance of the small Z cavity in the incorporation of larger cations by the ZR2+ → ZAl substitution. Relationships of direct proportionality between lattice parameters and both and are observed. The expansion of both octahedra, as well as of lattice parameters, increases linearly as a function of YMn2+ and ZMn2+. The latter has greater weight in dictating unit-cell variations, due to the degree of size mismatch between ZMn2+ → ZAl and YMn2+ → YLi substitutions, and the way in which the Z octahedra are articulated in the structure.
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The [9]-coordinated X site in tourmaline is usually occupied by Na, Ca, K, or is vacant. In contrast to earlier statements in the literature our recent evaluation of 81 tourmaline samples with Al on the Z site has clearly shown that the < X-O > distance, as could have been expected, is positively correlated to the average effective ionic radius of the X-site occupants (r = 0.98 for 81 tourmaline samples, with Al-6 at the Z site and (OH)(3) at the V site). Olenite and "oxy-rossmanite" samples, in which the V site is not completely occupied by OH, show a significant deviation to this correlation. X-site vacancies (up to similar to 0.7 apfu), as well as a significant variation of < T-O > and < Y-O > distances, do not seem to have a significant effect on the < X-O > distance. Tourmalines of the elbaite-olenite-rossmanite series (with Al-6 at the Z site) show a positive correlation between the < X-O > and the < Z-O > distance (r = 0.80; 40 samples) due to inductive effects in the structure.
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So-called "mushroom" tourmaline, a botryoidal aggregate of pale pink tourmaline crystals, occurs in the Palelni mine, Khetchel village, Molo quarter, Momeik Township, northeast of Mogok, Mandalay Division, Shan State, Myanmar. It has been characterized by crystal-structure determination, electron-microprobe analysis (EMPA), secondary-ion mass spectrometry (SIMS), uranium extraction, and inductively coupled plasma - mass spectrometry (ICP-MS). This sample consists of sprays of radially arranged crystals up to ∼9 mm in length and ∼50-150 μm in diameter. Chemical data show that Al increases, whereas the Mn content decreases, from the center of the aggregate to the pyramidal faces. The composition at the center can be described as a Mn-bearing elbaite with ∼1.6 wt% MnO. Near the pyramidal faces, the composition of these tourmaline crystallites is relatively Al-rich (up to 43.6 wt% Al2O3), and Mn-poor (0.1-0.3% MnO). A crystal-structure refinement of the Li-bearing olenite (near the pyramidal faces), in combination with analytical results, gives the optimized formula X(Na0.55 Ca0.08Pb0.01□0.36) Y(Al2.13Li0.75Mn2+0.01□0.11) ZAl6T(Si5.34B0.66)O18 (BO3)3V(OH)3W[(OH)0.50O0.26F0.24], with a 15.7561(6), c 7.0703(5) Å. The structure refinement yields a relatively high [4]B content (Si0.87(1) B0.13(1)), and a 〈T-O〉 distance of 1.604 Å, the shortest observed in natural tourmaline to date. Together with Al-rich tourmalines from other localities, a positive correlation between Al at Y site and [4]B with r2 ≈ 0.998 was found. Furthermore, this tourmaline aggregate shows a relatively high Pb content (1640 ppm) and a significant Bi content (153 ppm). The REE pattern (ΣREE: ∼7.2 ppm) exhibits a weak negative Eu anomaly, a strong positive Tm anomaly, and a positive Tb anomaly. Such a pattern cannot be derived simply from a late-stage fractionated magma of a S-type granite or from differentiated crustal melts alone.
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Physical, crystal-chemical and absorption spectroscopical properties of blue tourmalines from a new occurrence in the State of Paraiba, Brazil, are described. Refractive indices, birefringence and specific gravity have been determined as n e = 1.615–1.620, n o = 1.632–1.640, Δn =−0.017 to −0.020 and 3.04–3.07g/cm ³ . Microprobe analyses proved the samples to be elbaites, which are relatively Mn-rich and contain 2.1 wt. % CuO and 0.5 wt. % Bi 2 O 3 . Lattice constants are a o = 15.854(4) and c o = 7.102(1) Å. The blue colour is due to pleochroic absorption bands of Cu ²⁺ and Mn ³⁺ with maxima at 700 and 520 nm respectively.
Article
An Al-rich tourmaline from the Sahatany Pegmatite Field at Manjaka, Sahatany Valley, Madagascar, was structurally and chemically characterized. The combination of chemical and structural data yields an optimized formula of X (Na0.53Ca0.09□0.38) Y (Al2.00Li0.90Mn²⁺0.09Fe²⁺0.01) Z Al6 (BO3)3T [Si5.61B0.39]O18V (OH)3W [(OH)0.6O0.4], with a = 15.777(1), c = 7.086(1) Å (R 1 = 0.017 for 3241 reflections). The 〈T–O〉 distance of ∼ 1.611 Å is one of the smallest distances observed in natural tourmalines. The very short 〈Y–O〉 distance of ∼ 1.976 Å reflects the relatively high amount of Al at the Y site. Together with other natural and synthetic Al-rich tourmalines, a very good inverse correlation (r ² = 0.996) between [4]B and the unit-cell volume was found. [4]B increases with the Al content at the Y site approximately as a power function with a linear term up until [4]B ≈ Si ≈ 3 apfu and Y Al ≈ 3 apfu, respectively, in natural and synthetic Al-rich tourmalines. Short-range order considerations would not allow for [4]B in solid solution between schorl and elbaite, but would in solid solutions between schorl, "oxy-schorl", elbaite, liddicoatite, or rossmanite and hypothetical [4]B-rich tourmaline end-members with only Al³⁺ at the Y site. By plotting the [4]B content of synthetic and natural Al-rich tourmalines, which crystallized at elevated PT conditions, it is obvious that there are pronounced correlations between PT conditions and the [4]B content. Towards lower temperatures higher [4]B contents are found in tourmaline, which is consistent with previous investigations on the coordination of B in melts. Above a pressure of ∼ 1000–1500 MPa (depending on the temperature) the highest observed [4]B content does not change significantly at a given temperature. The PT conditions of the formation of [4]B-rich olenite from Koralpe, Eastern Alps, Austria, can be estimated as 500–700 MPa/630 °C.
Article
Columbite, beryl, lepidolite, and other economic minerals are associated with zoned pegmatites discordantly emplaced in Precambrian schists of the Alto Ligonha district, Mozambique. Mineral assemblages and textural features indicate that the pegmatites were formed by crystallization and differentiation in an essentially closed system; replacement processes may have played a part in formation of border zones and the lepidolite-albite zone adjacent to the quartz core.
Article
The crystal-chemistry of 13 elbaite-schorl tourmaline crystals from the Cruzeiro pegmatite (Minas Gerais, Brazil) was studied with a multi-analytical approach (SREF, EMPA, SIMS, MS). Effective cation radii at the Y and Z sites and site populations were refined by a minimization procedure. The results indicate that the crystals belong to the alkali group. Elbaite crystals are O2−-free at the W and V sites and show OH content at the O2 site (up to 0.2 apfu). Conversely, schorl crystals always show O2− at the W site. The main substitutional mechanism is the dehydroxylation type: The T site is characterized by TSi → TAl substitution. is linearly correlated with vacancy content in crystals with (OH + F) ≤ 4, whereas it is almost constant in crystals with OH at the O2 position. Along the series, is inversely correlated with YAl. The Z site is almost fully occupied by R3+ (with ZAl largely dominant) and the ZFetot ↔ ZAl substitution explains the inverse correlation of with ZAl. In the elbaite compositional range, lattice parameters are functions of , whereas in the schorl range they are essentially functions of . Along the whole elbaite-schorl series, both chemical substitutions and size increase of Y are far larger than those of Z. In spite of this, lattice parameters increase with as much as with . This is due to the role of the [ZO6] polyhedra, which extend along a and c to form the skeleton of the tourmaline structure. Therefore, any change in the size of Z leads to a change in the whole structure.
Article
The structure of an alkali cation-deflcient, vanadium tourmaline has been refined (R : 0.Ml for 2727 rntensity data) in order to evaluate the effects of tourmaline composition on structural distortion. V-tourmaline, (Nao*Ca.r"Mgo.,rIGor)(Mg,rrVlj"Ct'olrFe2o:r8) (Al5s6 V3*38Tit*o6XSi563Abj7XB2e8&or)Orr(O, roOH258Fo32), is rhombohedral with a : 15.967(2\ and c: 7.191(l)A; space group R3m. Despite compositional di-fferences the structure is very similar to those of other members of the tourmaline group, most notably a recently refined aluminous dravite. Analysis of tourmaline-group structural data reveals (l) a negative corre- lation between tetrahedral bond angle variance and mean "alkali'(3a)-oxygen bond length; (2) negative correlations between both 9b and l8c octahedral angle variances and mean 9b-O bond length; (3) a negative correlation between ditrigonality and 9b octahedral angle vari- ance; (4) a positive correlation between weighted mean octahedral bond length and cell vol- ume; and (5) a positive correlation between Na occupancy in the 3a site and mean 3a-O bond length. These observations demonstrate a systematic flexibility of the structure in response to diverse cation substitution. The lack of a distinct coupling between the sizes of the 9b and l8c octahedra in refined tourmaline structures and the extensive and possibly complete substitution of Al3* in the 9b site in tourmalines suggest that the presence of cations that can vary in size (e.g., ""2+' r+ ) in order to create a compatible edge may not be a prerequisite for dravite-elbaite solid solution. In view of the structural flexibility of tourmaline and the ease of proton exchange to maintain charge balance, the apparent immiscibility of dravite and elbaite is thought to reflect extreme fractionation of Mg and Li during petrogenesis and by the tourmaline structure, due to the large difference in the field strengths of these cations. Other major features of tourmaline sub- stitutional chemistry are also rationalized on the basis of cation field strength.
Article
The manner in which F is incorporated into the tourmaline structure depends on internal influences such as crystallographic constraints and on external influences such as temperature, pressure, local mineral assemblage and fluid composition. Tourmaline has a general formula XY(3)Z(6)(T6O18)(BO3)(3)V3W, with the most common site-occupancies being: X = Ca2+, Na1+, K1+, (X)square (vacancy); Y = Li1+, Mg2+, Fe2+, Mn2+, Al3+, Cr3+, Fe3+; Z = Al3+, Mg2+, Fe3+, Cr3+; T = Si4+, Al3+; B = B3+; V [O(3)] = OH1-, O2-; W [O(1)] = OH1-, F1-, O2-. Of particular importance for understanding F-1-incorporation in tourmaline is that F-1-occurs solely at the O(1) site. Substitution of F1-at this site is influenced by the occupancy (total charge) of the X and the Y sites. The X site is generally occupied by cations of variable charge (+1 or +2) or is vacant (zero charge). There are three Y-site cations, which can have charges of +1, +2, +3 or +4. However, the charge of the local bond-valence arrangements of the Y-site cations are most commonly between +6 (e.g., Mg-3) and +7 (e.g., Mg2Al). Because of local bonding of the O(1)-site anion to three neighboring Y-site cations and an X-site cation, the charges at the X and Y sites affect the F1-occupancy at the W site. Disorder of Mg and Al at the Y and Z sites influences the local charge, and consequently, the F content. The accumulated data on tourmaline verify the general crystallographic influences. A summary of > 8800 tourmaline compositions from different lithologic environments illustrates that for tourmaline with an average X-site charge exceeding +0.9, there is a range from 0 to a maximum of 1.0 apfu F. As the X-site charge decreases, the maximal amount of F decreases, with the maximal amount of F being less than 0.2 apfu for those tourmalines with an X-site charge of less than +0.5. Petrological factors superimpose local environmental influences on F concentrations. The presence of minerals with a fixed high F content, such as fluorite, local assemblages of minerals and the degree of fractionation in a magma or fluid control the amount of F that is available to tourmaline within the crystallographic constraints imposed by local X- and Y-site charge.
Article
Single-crystal structure and chemical (EMPA, SIMS, TGA) data were obtained from three pale coloured to colourless Al- and Li-rich tourmaline crystals from a pegmatite from Wolkenburg near Limbach-Oberfrohna, Saxony, Germany. Tourmaline samples of the "fluor-elbaite"-rossmanite solid solution series were chemically (including the light elements) and structurally characterized for the first time. The crystal chemical formulae of these three investigated samples range from a "fluor-elbaite" dominant composition with X(Na0.65□0.29Ca0.06)Y(Al1.64Li1.12Mn2+0.10Fe2+0.02□0.12)ZAl6(BO3)3T(Si5.90B0.10)O18(OH)3[F0.72(OH)0.18O0.10], over X(Na0.54□0.45Ca0.01)Y(Al1.90Li0.97Mn2+0.03Fe2+0.01□0.09)ZAl6 (BO3)3T(Si5.82B0.18)O18V(OH)3W[(OH)0.51F0.37O0.12] to Na-rich rossmanite with the composition X(□0.51Na0.48Ca0.01)Y(Al2.02Li0.71Mn2+0.03□0.24)ZAl6(BO3)3T(Si5.69Al0.17B0.14)O18V(OH)3W[(OH)0.70F0.26O0.04]. When the rossmanite component increases, while the "fluor-elbaite" component decreases, the olenite component also increases. In a pegmatitic system where essentially no Fe, Mn, Ti and Mg are available, the Li content is an important factor, which seems to control the amount of Si in tourmaline. Once the Li1+ content is lower, Al3+ cations (with a higher oxidation state) must occupy the Y site. For a charge-balanced formula, other cation sites must therefore have lower bulk charges. This can be achieved by increasing vacancies at the X site and increasing amounts of trivalent cations at the T site. In the Wolkenburg tourmalines of the "fluor-elbaite"-rossmanite series both substitutions are observed. For our investigated tourmalines we can propose a modified (coupled) Tschermaks' substitution with X□ + YAl3+ + T(Al, B)3+ ↔ XNa+ + YLi+ + TSi4+. The F content is dependent on the charge of the X-site occupants. There is also a good negative correlation between the charge of the X-site occupants and the X-O2 distance, which can be used to draw some conclusions about the X-site occupancy when only single-crystal structure data are available.
Article
Optical absorption spectra are presented for taramellite, traskite and neptunite, all of which have both Fe2+ and Ti4+ as major elements. The spectra of each of these minerals are dominated by a single, intense absorption band in the 415 to 460 nm region with 7000 to 9000 cm–1 halfwidth. These transitions, assigned to Fe2+-Ti4+ intervalence charge transfer, showed little difference in intensity at 80 and 300 K and have molar absorptivities which range from 100 to 1300 M–1 cm–1. The Fe2+-Ti4+ absorptions in these standards generally compare well to other mineral spectra in which Fe2+ — Ti4+ intervalence absorption has previously been proposed with the exception of the most cited example, blue corundum.
Article
Pale-blue to pale-green tourmalines from the contact zone of Permian pegmatites to mica schists and marbles from different localities of the Austroalpine basement units (Rappold Complex) in Styria, Austria, are characterized. All these Mg-rich tourmalines have small but significant Li contents, up to 0.29wt% Li2O, and can be characterized as dravite, with FeO contents of  ~ 0.9–2.7wt%. Their chemical composition varies from X (Na0.67Ca0.19 K0.02☐0.12) Y (Mg1.26Al0.97Fe2+ 0.36Li0.19Ti4+ 0.06Zn0.01☐0.15) Z (Al5.31 Mg0.69) (BO3)3 Si6O18 V (OH)3  W [F0.66(OH)0.34], with a = 15.9220(3), c = 7.1732(2) Å to X (Na0.67Ca0.24 K0.02☐0.07) Y (Mg1.83Al0.88Fe2+ 0.20Li0.08Zn0.01Ti4+ 0.01☐0.09) Z (Al5.25 Mg0.75) (BO3)3 Si6O18 V (OH)3  W [F0.87(OH)0.13], with a = 15.9354(4), c = 7.1934(4) Å, and they show a significant Al-Mg disorder between the Y and the Z sites (R1 = 0.013–0.015). There is a positive correlation between the Ca content and < Y-O > distance for all investigated tourmalines (r ≈ 1.00), which may reflect short-range order configurations including Ca and Fe2+, Mg, and Li. The tourmalines have XMg (XMg = Mg/Mg + Fetotal) values in the range 0.84–0.95. The REE patterns show more or less pronounced negative Eu and positive Yb anomalies. In comparison to tourmalines from highly-evolved pegmatites, the tourmaline samples from the border zone of the pegmatites of the Rappold Complex contain relatively low amounts of total REE (~8–36ppm) and Th (0.1–1.8ppm) and have low LaN/YbN ratios. There is a positive correlation (r ≈ 0.91) between MgO of the tourmalines and the MgO contents of the surrounding mica schists. We conclude that the pegmatites formed by anatectic melting of mica schists and paragneisses in Permian time. The tourmalines crystallized from the pegmatitic melt, influenced by the metacarbonate and metapelitic host rocks.
Article
Microanalytical trace element techniques (such as ion probe or laser ablation ICP-MS) are hampered by a lack of well characterized, homogeneous standards. Two silicate glass reference materials produced by National Institute of Standards and Technology (NIST), NIST SRM 610 and NIST SRM 612, have been shown to be homogeneous and are spiked with up to sixty one trace elements at nominal concentrations of 500 mu g g(-1) and 50 mu g g(-1) respectively. These samples (supplied as 3 mm wafers) are equivalent to NIST SRM 611 and NIST SRM 613 respectively (which are supplied as 1 mm wafers) and are becoming more widely used as potential microanalytical reference materials. NIST however, only certifies vp to eight elements in these glasses. Here we have compiled concentration data from approximately sixty published works for both glasses, and have produced new analyses from our laboratories. Compilations are presented for the matrix composition of these glasses and for fifty eight trace elements. The trace element data includes all available new and published data, and summaries present the overall average and standard deviation, the range, median, geometric mean and a preferred average (which excludes all data outside +/- one standard deviation of the overall average). For the elements which have been certified, there is a good agreement between the compiled averages and the NIST data. This compilation is designed to provide useful new working values for these reference materials.