Roberta Oberti's research while affiliated with Diamond Light Source and other places
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Publications (176)
Al Pizzo Marcio in Val Vigezzo (Verbano-Cusio-Ossola, Piemonte), nelle albititi che sullo stesso monte, nel versante nord, ospitano i berilli verdi (smeraldi), è stata accertata la presenza di un raro anfibolo ortorombico di litio, holmquistite, ☐Li2(Mg3Al2)Si8O22(OH)2. In aggregati divergenti e disordinati di cristalli vitrei allungati finemente f...
The amphiboles from Kakanui and Arenal are two natural minerals have been used worldwide as microanalytical reference materials, but their compositions and crystal structures are still poorly constrained. In this paper, we report new data on H2O and trace element mass fractions and single‐crystal structural refinement of these two amphiboles. H2O m...
In this work we address the stability of riebeckite at high temperatures and compare the different behaviors observed under various oxidation conditions. For this purpose, we annealed powders of a sample from Mt. Malosa (Malawi), which is compositionally close to the end-member; the run products obtained after annealing in air vs. in vacuum were st...
Ferro-papikeite, ideally NaFe22+(Fe32+Al2)(Si5Al3)O22(OH)2, is a new mineral of the amphibole supergroup from the Filipstad Municipality, Värmland County, Central Sweden, where it occurs in a medium-grade felsic metavolcanic rock. Ferro-papikeite is pale brown with a translucent luster, has a colorless to very pale-brown streak, and shows no fluore...
Amphiboles are essential components of the continental crust and subduction zones showing anomalous anisotropic conductivity. Rock properties depend on the physical properties of their constituent minerals, which in turn depend on the crystal phonon and electron density of states. Here, to address the atomic-scale mechanism of the peculiar rock con...
The thermoelastic behavior of a crystal of Fe-rich holmquistite with crystal-chemical formula A(K0.01Na0.01)B(Li1.88Mg0.10Na0.02)C(Mg1.68Fe1.422+Mn0.022+Al1.88)TSi8.00O22W[(OH)1.97F0.03] was studied by single-crystal X-ray diffraction at temperatures up to 1023 K, where isothermal annealing in air for 160 h yielded the loss of 0.85 H apfu coupled w...
To univocally identify mineral species on the basis of their formula, the IMA-CNMNC recommends the use of the dominant-valency rule and/or the site-total-charge approach, which can be considered two procedures complementary to each other for mineral identification. In this regard, several worked examples are provided in this study along with some s...
The chapters contributed to the volume recognize the important and diverse contributions of mineralogy to the valorization, characterization, interpretation and conservation of cultural heritage. The book focuses on examples of materials and methodological issues rather than technical/analytical details. We have attempted to deal with the cultural...
Potassic-jeanlouisite, ideally K(NaCa)(Mg 4 Ti)Si 8 O 22 O 2 , is the first characterised species of oxo amphibole related to the sodium–calcium group, and derives from potassic richterite via the coupled exchange C Mg –1W${\rm OH}_{{\rm \ndash 2}}^{\ndash}{} ^{\rm C}{\rm Ti}_1^{{\rm 4 +}} {} ^{\rm W}\!{\rm O}_2^{2\ndash} $ . The mineral and the mi...
Potassic-jeanlouisite, ideally K(NaCa)(Mg 4 Ti)Si 8 O 22 O 2 , is the first characterised species of oxo amphibole related to the sodium-calcium group, and derives from potassic richterite via the coupled exchange C Mg-1 W OH-2 C Ti 4+ 1 W O 2-2. The mineral and the mineral name were approved by the International Mineralogical Association Commissio...
We present the results of a comprehensive study linking the crystal‐chemical formulae of amphiboles, a series of extremely complex silicates with the general formula (AB2C5T8O22W2, C5 = M12M22M3) to variations in the peak positions, widths, and intensities of the Raman‐active modes. To this purpose, we have analyzed the Raman scattering generated b...
Ferri-fluoro-katophorite is the second species characterised involving the rootname katophorite in the sodium-calcium subgroup of the amphibole supergroup. The mineral and its name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification, IMA2015-096. It was found in the Bear Lake digg...
Potassic-jeanlouisite, ideally K(NaCa)(Mg 4 Ti)Si 8 O 22 O 2 , is the first characterised species of oxo amphibole related to the sodium-calcium group, and derives from potassic richterite via the coupled exchange C Mg-1 W OH-2 C Ti 4+ 1 W O 2-2. The mineral and the mineral name were approved by the International Mineralogical Association Commissio...
We report polarized Raman spectra from potassic-magnesio-arfvedsonite in all informative scattering configurations. On the basis of the polarization selection rules, several Ag vibrational modes have been identified. The Bg modes, however, are below the detection limits of the Raman spectrometer. The OH stretching band is situated between 3630 and...
The chapters contributed to the volume recognize the important and diverse contributions of mineralogy to the valorization, characterization, interpretation and conservation of cultural heritage. The book focuses on examples of materials and methodological issues rather than technical/analytical details. We have attempted to deal with the cultural...
Magnesio-hornblende (IMA2017-059) has been characterized in a specimen collected in the sand dunes of Lüderitz, Karas Region, Namibia. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is A (□ 0.73 Na 0.22 K 0.05) Σ1.00 B (Ca 1.79 Fe 2+ 0.10 Mg 0.04 Mn 2+ 0.03 Na 0.04) Σ2.00 C (Mg 3.48 Fe 2+ 0.9...
In this work we report on a complete crystal-chemical characterization of a near end-member riebeckite from Malawi, and use the available data to critically compare information obtained from different analytical methods. The sample occurs as well-formed and very large single crystals in pegmatitic rocks. Accurate site-populations were determined by...
We investigated the oxidation behaviour of a synthetic potassic-ferro-richterite up to 750° C by using simultaneous X-ray absorption spectroscopy and X-ray diffraction experiments with synchrotron radiation. From X-ray diffraction we observed an abrupt drop of cell dimensions ~335° C accompanied by an anomalous increase in the monoclinic cell angle...
The complete mineral description of potassic-magnesio-arfvedsonite, a recently approved (IMA2016-083) new species of the amphibole supergroup is provided using electron microprobe analysis (EMPA), laser ablation inductively coupled plasma mass spectrometry, single-crystal structure refinement, Mössbauer and Raman spectroscopy, as well as measuremen...
Ferri-fluoro-katophorite is the second species characterised involving the rootname katophorite in the sodium–calcium subgroup of the amphibole supergroup. The mineral and its name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification, IMA2015-096. It was found in the Bear Lake digg...
In this work, we investigate the oxidation behavior of a nearly end-member riebeckite, ideally Na2 (Fe3²⁺Fe2³⁺) Si8O22(OH)2, by using vibrational FTIR and Raman spectroscopies. Combining these results with previous studies performed on the same sample by single-crystal structure refinement and Mössbauer spectroscopy, we conclude that iron oxidation...
In this work, we have studied the relationships between mass concentration and unit formula of amphibole using 114 carefully selected high-quality experimental data, obtained by electron microprobe (EMP) + single-crystal X-ray structure refinement (SREF) ± secondary-ion mass spectrometry (SIMS) analyses, of natural and synthetic Li-free monoclinic...
The HT behaviour of a well-characterized sample of riebeckite has been examined by combining X-ray diffraction, FTIR 18 and Mössbauer spectroscopy. The crystal-chemical composition of the crystal studied is: A (K 0.05 Na 0.04) B ðNa 1:86 Ca 0:09 Fe 2þ 0:05 Þ 19 C ðFe 2þ 2:94 Mg 2þ 0:22 Mn 2þ 0:02 Zn 2þ 0:01 Fe 3þ 1:74 Al 3þ 0:06 Ti 4þ 0:01 Þ T (Si...
The mineral description is provided for ferro-tschermakite, ideally A ☐ B Ca 2 C (Fe 2þ 3 Al 2) T (Si 6 Al 2)O 22 W (OH) 2. The type specimen has been found in the dump of the Bâtiment et Granit de Ploumanac'h northern granite quarry, La Clarté, Perros-Guirec, Ploumanac'h granitic complex, Brittany, France. The empirical formula derived from electr...
Clino-suenoite, ideally □Mn 2þ 2 Mg 5 Si 8 O 22 (OH) 2 is a new amphibole of the magnesium-iron-manganese subgroup of the amphibole supergroup. The type specimen was found at the Lower Scerscen Glacier, Valmalenco, Sondrio, Italy, where it occurs in Mn-rich quartzite erratics containing braunite, rhodonite, spessartine, carbonates and various acces...
Davidsmithite, a newly approved feldspathoid mineral (IMA 2016-070), occurs as a rock-forming mineral in the Liset eclogite pod (Norwegian Caledonides). It is transparent, colourless, uniaxial negative, v = 1.538(2), e = 1.535(2). No cleavage was observed. Davidsmithite is hexagonal, space group P63 and has unit-cell dimensions: a = 9.982(1) A ; c...
Magnesio-riebeckite from the dumps of the abandoned mine of Varenche (45°47'22'' N, 7°29'17'' E), Saint-Barthélemy, Nus, Aosta Valley (Italy), was studied to provide the complete mineral description (including crystal structure) and insights into the crystal-chemistry of riebeckite. The empirical formula derived from electron microprobe analysis an...
New chemical (EMP, SIMS) and structural data are reported for a suite of crystals of oxo-mangani-leakeite and mangano-mangani-ungarettiite from their common type locality, the Hoskins mine (New South Wales, Australia). Notwithstanding the low OH content, FTIR analysis of selected samples has provided considerable information on short-range order in...
Ferro-ferri-hornblende is a new member of the amphibole supergroup (IMA-CNMNC 2015-054). It has been found in a rock specimen from the historical collection of Leandro De Magistris, which was collected at the Traversella mine (Val Chiusella, Ivrea, Piemonte, Italy). The specimen was catalogued as 'speziaite', and contains a wide range of amphibole...
IMA No. 2016-116
Ferro-tschermakite
□Ca2(Fe2+3Al2)(Si6Al2)O22(OH)2
Granite quarries, La Clarté, Perros-Guirec,
Ploumanac’h Granitic Complex, Bretagne,
France (48°48′50″N, 3°28′50″W)
Roberta Oberti*, Massimo Boiocchi, Frank
C. Hawthorne and Marco E. Ciriotti
*E-mail: oberti@crystal.unipv.it
Amphibole supergroup
Monoclinic: space group C2/m; structur...
Pink-orange crystals of a composition within the ferri-obertiite compositional space were found in vesicles in a pale beige silicate vein found from a basalt quarry at Mount Rothenberg, Eifel district, Germany. Associated minerals are potassic feldspar, alpha quartz paramorphic after beta quartz, eifelite (the second occurrence after the Caspar qua...
Clino-suenoite, ideally ☐Mn2+ 2Mg5Si8O22(OH)2 is a new amphibole of the magnesium iron-manganese subgroup of the amphibole supergroup. The type specimen was found at the Lower Scerscen Glacier, Valmalenco, Sondrio, Italy, where it occurs in Mn-rich quartzite erratics containing braunite, rhodonite, spessartine, carbonates and various accessory mine...
In order to characterize the role of Ti in the crystal structure of calcium amphiboles with high or even dominant oxo-component, the crystal structure of a Ti-rich calcium amphibole from a gabbro at Kaersut, Greenland, has been refined with single-crystal MoKα X-ray intensity data to an R1(F) index of ~0.025, and with single-crystal Laue neutron in...
High-temperature Fourier transform infrared (HT-FTIR) spectroscopy was used to characterize the deprotonation process of synthetic potassic-ferro-richterite of composition A(K0.90Na0.07)B(Ca0.54Na1.46) c F e 4.22 2 + F e 0.78 3 + T S i 8 O 22 W O H 1.70 O 0.30 2 - ^{\rm{c}}{\left( {{\rm{Fe}}-{4.22}^{2 + }{\rm{Fe}}-{0.78}^{3 + }} \right)^{\rm{T}}}{\...
During systematic characterization of amphiboles that still lack a complete mineral description, fluoro-tremolite was identified in a specimen from the Limecrest-Southdown quarry, Sparta, New Jersey, USA, which was provided by the Franklin Mineral Museum. The ideal formula of fluoro-tremolite is A □ B Ca 2C Mg 5T Si 8 O 22W F 2 and the empirical fo...
In this work we report on a complete crystal-chemical characterization of a near end-member riebeckite from Malawi, and use the available data to critically compare information obtained from different analytical methods. The sample occurs as well-formed and very large single crystals in pegmatitic rocks. Accurate site-populations were determined by...
Ferro-ferri-hornblende is a new member of the amphibole supergroup (IMA-CNMNC 2015-054). It has been found in a rock specimen from the historical collection of Leandro De Magistris, which was collected at the Traversella mine (Val Chiusella, Ivrea, Piemonte, Italy). The specimen was catalogued as 'speziaite', and contains a wide range of amphibole...
Oxo-mangano-leakeite, a newly approved end-member of the amphibole supergroup (IMA-CNMNC 2015-035), has been found in a rock containing manganese silicate and oxide at the Hoskins Mine, a Mn deposit 3 km west of Grenfell, New South Wales. The end-member formula of oxo-mangani-leakeite is A Na B Na 2 C (Mn 3þ 4 Li) T Si 8 O 22 W O 2 , which would re...
Microanalysis of Fe3+/∑Fe in geological samples using synchrotron-based X-ray absorption spectroscopy has become routine since the introduction of standards and model compounds. Existing calibrations commonly use least-squares linear combinations of pre-edge data from standard reference spectra with known coordination number and valence state acqui...
Magnesio-ferri-fluoro-hornblende has the ideal formula A □ B Ca 2 C (Mg 4 Fe 3+) T (Si 7 Al)O 22 W F 2 (Hawthorne et al., 2012). The holotype sample described in this work occurs as prismatic crystals in vugs of volcanic rocks (Seruci ignimbrites), found along the coast road ∼5.5 km northeast of Portoscuso, Cagliari, Sardinia; associated minerals a...
The high-temperature behavior of synthetic potassic-ferro-richterite was addressed to obtain data relevant to understanding petrogenetic processes as well as to testing complementarity and mutual calibration of single-crystal X-ray diffraction (XRD) analysis plus structure refinement (SREF) with single-crystal FTIR spectroscopy. This experimental a...
The crystal-chemical characterization of an amphibole with an unusual composition, A(Na0.76K0.24)B(Ca1.42Na0.56Mn2+0.02)C(Mg2.64Fe2+1.95Mn2+0.07Mg2.64Zn0.01Fe3+0.01Ti4+0.32)T(Si7.18Al0.82)O22W[(OH)0.58O0.27F1.15], found in pegmatitic veins at Kariåsen, Larvik Plutonic Complex, Norway, provides an excellent example of the detection and estimation of...
In the paper on which we are commenting ([Joy & Evans 2014][1]), the authors (hereafter referred to as J&E) introduced a new mineral belonging to the amphibole supergroup, gave it a name, and discussed its relations with coexisting amphiboles and amphiboles reported in previous literature.
First,
Following the characterization of the new amphibole species fluoro-leakeite, ideally ANa BNa2 C(Mg2Al2Li) TSi8 O22 WF2, at Norra Kärr (Sweden), so far considered the type locality of eckermannite, re-examination of the holotype material of
eckermannite deposited at the Museum of Natural History in London (BM 1949.151) and of the original sample ana...
Katophorite has the ideal formula A Na B (NaCa) C (Mg 4 Al) T (Si 7 Al)O 22 W (OH) 2 (Hawthorne et al., 2012). No published analyses of amphiboles fall in the katophorite compositional field, except that of Harlow and Olds (1987) for an amphibole from near Hpakan in the Jade Mine Tract, Myanmar. This amphibole was approved by the International Mine...
Magnesio-arfvedsonite, the C Fe 3+-dominant analogue of eckermannite, has been found in a sample of ''szechenyite'' in the mineral collection of the American Museum of Natural History (AMNH H35024). It comes from the northern part of the Jade Mine Tract near Hpakan, Kachin State, Myanmar. Associated minerals are kosmochlor-jadeite solid-solution py...
In order to clarify details of volatiles incorporation in arrojadites, two samples previously characterized by X-ray diffraction and electron-microprobe (EMP) and LA-ICPMS analysis were investigated by single-crystal FTIR spectroscopy. The present study confirms and makes more quantitative previous results by single-crystal structure refinement abo...
The first edition of the ECA European Crystallography School (ECS1), to be held in Pavia (Italy) during the course of IYCr2014, has found good balance between two apparently diverging goals: (i) to help students and young researchers to find their way in modern science, while keeping a special focus on the molecular and crystalline structure to int...
In this study we address the crystal-chemistry of a set of five samples of
F-rich amphiboles from the Franklin marble (USA), using a combination of
microchemical (EMPA), SREF, and FTIR spectroscopy methods. The EMPA data show
that three samples fall into the compositional field of fluoro-edenite whereas
two samples are enriched in high-charged C ca...
Actinolite and glaucophane are the principal amphiboles in greenschist- and blueschist-facies metamafic rocks, respectively, and constitute an important mineral pair for deducing the conditions of medium- and high-pressure metamorphism. Here we present the crystal-chemical properties of amphiboles synthesized along the tremolite glaucophane join as...
A new classification and nomenclature scheme for the amphibole-supergroup minerals is described, based on the general formula AB 2 C 5 T 8 O 22 W 2 , where A = o, Na, K, Ca, Pb, Li; B = Na, Ca, Mn 2+ , Fe 2+ , Mg, Li; C = Mg, Fe 2+ , Mn 2+ , Al, Fe 3+ , Mn 3+ , Ti 4+ , Li; T = Si, Al, Ti 4+ , Be; W = (OH), F, Cl, O 2-. Distinct arrangements of form...
A new classification and nomenclature scheme for the amphibole-supergroup minerals is described, based on the general formula AB 2 C 5 T 8 O 22 W 2 , where A = o, Na, K, Ca, Pb, Li; B = Na, Ca, Mn 2+ , Fe 2+ , Mg, Li; C = Mg, Fe 2+ , Mn 2+ , Al, Fe 3+ , Mn 3+ , Ti 4+ , Li; T = Si, Al, Ti 4+ , Be; W = (OH), F, Cl, O 2-. Distinct arrangements of form...
A new classification and nomenclature scheme for the amphibole-supergroup minerals is described, based on the general formula AB(2)C(5)T(8)O(22)W(2), where A = square, Na, K, Ca, Pb, Li; B = Na, Ca, Mn2+, Fe2+, Mg, Li; C = Mg, Fe2+, Mn2+, Al, Fe3+, Mn3+, Ti4+, Li; T = Si, Al, Ti4+, Be; W = (OH), F, Cl, O2-. Distinct arrangements of formal charges a...
Rift-related Cenozoic alkaline mafic lavas from northern Victoria Land (Antarctica), carry abundant mantle xenoliths whose oxygen fugacities (fO2) were determined to assess how the metasomatism, related to Cenozoic magmatism, affected the state of oxidation of the lithospheric mantle. The xenoliths used for this study are anhydrous spinel peridotit...
The thermoelastic behaviour of a natural gedrite having the crystal-chemical formula ANa0.47B(Na0.03 Mg1.05 Fe
0.862+ Mn0.02 Ca0.04) C(Mg3.44 Fe
0.362+ Al1.15 Ti
0.054+) T(Si6.31 Al1.69)O22W(OH)2 has been studied by single-crystal X-ray diffraction to 973 K (Stage 1). After data collection at 973 K, the crystal was heated to 1,173 K to induce dehyd...
The symmetry and crystal chemistry of a(OH,F)-rich spessartine from Junzico Xijang, Wushan Spessartine Mine, Yunxiao Co., Fujian Province, P.R. China, with composition (X)(Mn2.872+Fe0.092+Ca0.04) (Y)(Al-1.Fe-94(0.06)3+) (Z)[(SiO4)(2.52) (OH1.11F0.81)] have been studied by single-crystal X-ray structure refinement and FTIR spectroscopy. This sample...
The thermoelastic behaviour of anthophyllite has been determined for a natural crystal with crystal-chemical formula ANa0.01
B(Mg1.30Mn0.57Ca0.09Na0.04) C(Mg4.95Fe0.02Al0.03) T(Si8.00)O22
W(OH)2 using single-crystal X-ray diffraction to 973K. The best model for fitting the thermal expansion data is that of Berman
(J Petrol 29:445–522, 1988) in whic...
Fluoro-aluminoleakeite is a new mineral of the amphibole group from Norra Kärr, Sweden (IMA-CNMMNC 2009-012). It occurs in a proterozoic alkaline intrusion that mainly comprises a fine-grained schistose agpaitic nepheline-syenite (grennaite). Fluoro-aluminoleakeite occurs as isolated prismatic crystals 0.10À2 mm long in a syenitic matrix. Crystals...
Potassic-aluminotaramite, ideally (A)K (CaNa) (B)(Fe(3)(2+)Al(2)) (C)(Si(6)Al(2)) O(22) (W)(OH)(2), has been found in a meta-monzonite rock sampled at Sierra de los Filabres, S.E. Spain; the paragenesis that contains the amphibole is mainly formed by feldspar, quartz, and clinopyroxene. This paper reports a complete mineral description and crystal-...
This paper describes a multi-technique approach to the complete crystal-chemical characterization of a gadolinite-(Y) sample found in a volcanic holocrystalline ejectum near the Vico lake (Latium, Italy). Gadolinite-(Y) occurs as poly-twinned crystals forming rounded short-prismatic aggregates (generally 0.1-0.3 mm in size, with the largest ever fo...
The crystal structure of eight sodic-calcic and sodic amphiboles from the Kajlidongri manganese mine, India, have been refined to R values of 1-2% using single-crystal MoK alpha X-ray data. The crystals used in