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(a) The ternary plot of Ca 2+ − Na + −X-site vacancy is used to classify the principal groups of tourmaline based on X-site occupancy (Henry et al., 2011). All of the samples belong to the alkali group. (b) The ternary diagram 2Li + −Mg 2+ −Fe 2+ for Y-site occupancy of alkali-group tourmalines indicates that all of the analysed samples are elbaite. The colour of the symbols broadly correlates with the colour of the tourmaline.

(a) The ternary plot of Ca 2+ − Na + −X-site vacancy is used to classify the principal groups of tourmaline based on X-site occupancy (Henry et al., 2011). All of the samples belong to the alkali group. (b) The ternary diagram 2Li + −Mg 2+ −Fe 2+ for Y-site occupancy of alkali-group tourmalines indicates that all of the analysed samples are elbaite. The colour of the symbols broadly correlates with the colour of the tourmaline.

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Article
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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....

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Context 1
... never exceeds 1 wt.%. Thus, based on their X-site occupancy, all of the tourmalines belong to the alkali group (Henry et al., 2011; Figure 8a) with 0.56-0.83 apfu Na, up to 0.15 apfu Ca and up to 0.38 apfu vacancies. ...
Context 2
... Na, up to 0.15 apfu Ca and up to 0.38 apfu vacancies. Within the alkali group, all samples plot in the elbaite field, and most of them are close to the elbaite end member (Figure 8b). ...
Context 3
... Brazilian samples exhibit a strong variation between 0.3 and 84 ppm Mg, with distinctly higher contents of 139, 841 and 3,637 ppm in samples BRA3, BRA6 and BRA10, corresponding to 0.02-0.60 wt.% MgO (Table I; Figure 8b). Lower Mg contents were recorded in the Mozambique tourmalines, in which Mg is below the detection limit in seven samples and, for the remaining 11 pieces, only three yielded >1 ppm (i.e. up to 2.7 ppm and an exceptional value of 133 ppm in MOZ17; see Table II). ...

Citations

... There was no clear-cut correlation of the Cu and Mn contents with coloration. The blue color was in most cases due to Cu2+ (Okrusch et al, 2015). Pink and violet coloration (due to Mn3+) was shown by Mnbearing tourmalines that contained no significant Fe. Green color in the Nigerian tourmaline was most probably due to a combination of Mn, Cu, and Fe. ...
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Article
Gemstones are a special class of industrial minerals that are cut or faceted and polished for use as jewelry and other personal adornments. Gemstones are adorable objects that are desired and sought after by both royalty and the wealthy for their unique properties including beauty and color, luster and sparkle, durability and hardness, and extreme rarity. Gemstones, on the other hand, are minerals that constitute part of a country's natural endowment to be explored, exploited and revenues used for community benefit. Nigeria is endowed with substantial gemstone resources and the only country in Western Africa with commercial deposits of precious and semi-precious stones including Paraiba tourmaline, sapphire, emerald, aquamarine, spessartite and rhodolite garnets, beryl, topaz, amethyst, zircon, and a couple of rare species such as ruby, phenakite, kunzite, tanzanite, tsavorite and lepidolite. Most of the gemstones are mined mostly "informally" from weathered rocks and associated eluvial and alluvial deposits by artisanal and small scale miners who are virtually illiterate individuals who sell their raw gems for quick cash with no value added. There are no records of production, and little or no revenue gets into the Federal Government coffers. This paper presents an overview of the geological occurrence, distribution, provenance and origin of Nigerian gemstones, and the potential application of the knowledge in gem prospecting and exploration. There is an urgent need for government reforms of artisanal mining and active regulation of the gemstone industry so that all the loopholes and leakages in the gem supply pipeline and value chain are fixed for the utmost benefit of the Nigerian economy,
... Natural minerals and pure oxide standards were selected for calibration, and automatic ZAF corrections were applied before the results were reported in oxide form. The atomic (Clark 2007;Henry et al. 2011;Okrusch et al. 2016) assuming O 2-, Fand OHto be allocated proportionally in the V site and W site. Although Li and O cannot be detected by EPMA, they can be estimated from the ideal formula for elbaite. ...
... Ti, Mn, Fe, Mg, Zn and Pb) filling this site fully, which is based on a total of 15 atoms per formula unit (apfu) allocated in the T site, Y site and Z site (Shirose & Uehara 2013). Moreover, OH was calculated according to the formula OH + F = 4 apfu, as suggested by Clark (2007), Henry et al. (2011) and Okrusch et al. (2016). The content of B 2 O 3 was recalculated by assuming stoichiometry with B = 3 apfu (Henry et al. 2011). ...
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Article
Saturated pink-to-red tourmaline is a desirable gem material and therefore pale stones are commonly enhanced by gamma irradiation to intensify the red colour. For this study, 20 tourmalines from Nigeria ranging from near-colourless to pale pink, pink and pale orangey pink were subjected to electron-beam and gamma irradiation. Each sample was cut into two pieces for irradiation by each treatment method at three dose levels (i.e. 400, 800 and 1200 kilograys). During treatment, the samples turned pink to intense pink and orangey pink to pinkish orange or yellowish orange, with more intense colouration produced by electron-beam irradiation. The UV-Vis spectra of the irradiated tourmalines showed a maximum absorption feature centred at around 510–520 nm (due to Mn3+) and a minor band at about 395 nm also attributed to Mn (probably Mn3+), which caused the pink colouration. Yellow colouration seen in some samples after irradiation was probably contributed by the O– hole centre. Features associated with both the O– hole centre and H0 electron centre were present in the EPR spectra of the irradiated samples.
... The chemistry of natural Cu-bearing tourmalines with significant amounts of Bi (up to ~0.5-0.8 wt% Bi2O3) was described by [25][26][27][28]. The highest amount of Bi (~1.5 wt% Bi2O3) in Cu-bearing tourmaline was described by [29]. ...
... The chemistry of natural Cu-bearing tourmalines with significant amounts of Pb (up to ~0.4 wt% PbO) was described by [28]. Tourmalines (fluor-liddicoatite; Cu below the detection limit) with up to ~0.6 wt% PbO were described by [31] from a granitic pegmatite in Madagascar. ...
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Article
Copper- and Mn-bearing elbaitic tourmaline (“Paraíba tourmaline”) sometimes contains significant amounts of Pb and Bi. Their position in the tourmaline crystal structure was studied with correlation analysis and bond valence calculations. Correlations between the F content and the X-site charge allow predicting the X-site occupancy. Three sets of tourmaline analyses were studied: (1) Pb-rich tourmalines from the Minh Tien pegmatite, Vietnam; (2) Cu-, Pb- and Bi-bearing tourmalines from the Mulungu mine, Brazil; (3) Cu- and Bi-bearing tourmalines from the Alto dos Quintos mine, Brazil. Two correlations were plotted: (1) the charge by considering only Na1+, Ca2+ and K1+; (2) the charge by adding Pb2+ and Bi3+ to the X-site charge. When plotting correlations for the Minh Tien tourmalines, the correlation significantly improves by adding Pb2+ to the X site. For the Alto dos Quintos tourmalines, only a slight increase of the correlation coefficient is observed, while such a correlation for tourmalines from Mulungu interestingly shows a slight decrease of the correlation coefficient. Bond valence calculations revealed that Bi3+ and Pb2+ can indeed occupy the X site via BiLi(NaAl)−1, PbLi(NaCu)−1 and possibly PbCu(NaAl)−1 substitutions as seen in the investigated tourmaline samples. At the Y site, Pb4+ can be substituted via PbLi(AlCu)−1, and PbVO(AlVOH)−1, while Bi5+ does not have any stable arrangement in Cu-bearing fluor-elbaite. The occurrence of Pb4+ at the Y site could be one explanation for the results of the correlations of the Mulungu tourmalines. Another explanation could be that during the tourmaline crystallization some additional Bi and Pb came into the pegmatitic system and hence disturbed the correlation between the average X-site charge and the F content. Further plots of such correlations in “Paraíba tourmaline” samples might also help to distinguish between the worldwide localities of these rare and sought-after tourmalines.
... The typical blueish-green, greenish-blue and "neon-blue" hues are seen as a consequence Cu-and Mn-abundance, which has been discussed extensively in previous publications (e.g. Okrusch et al., 2016;Perretti et al., 2009 and references therein). The analysed tourmalines display a blueish shade of green and contain both Mn as well as high amounts of Cu like the blue samples and elevated amounts of Fe, analogous to the green samples. ...
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Conference Paper
Granitic pegmatites from the Borborema province in the state of Rio Grande do Norte in northeastern Brazil are amongst the most essential sources of tantalum, beryllium and gemstones, such as "Paraíba-type" tourmaline. According to LA-ICP-TOF-MS analysis and subsequent geochronological investigation performed on zircon, the genesis of the LCT-type Boqueirão granitic pegmatite has been confirmed to have occurred in a late stage of the Brasiliano-Pan-African orogeny in the Late Cambrian, 491±26 Ma ago (see fig. 1), which is in agreement with a recently published paper by Strmic Palinkas et al. (2019). The core of zoned garnet crystals indicate initiating crystallisation from the melt in the wet-solidus range of granite, as garnet-phengite geothermobarometry yielded temperatures of 711-763°C (± 60°C). Measurements of the rim revealed temperatures of 619-664°C (± 60°C) and thus suggest a retrograde cooling. This observation is supported by the presence of secondary clinozoisite-epidote, zoisite and prehnite, which are indicative of overprints in the greenschist and the prehnite-pumpellyite facies, respectively. Moreover, the proceeding crystallisation of mostly water-free minerals led to accumulation of hydrothermal fluids, resulting in alterations in mineralogy such as complete replacement of kalifeldspar by clay or evolution of hydrothermal zircon. Late selective replacement of zoned elbaite by Li-bearing mica has been observed. As previously described by Beurlen et al. (2011), the purple core experienced the highest amount of replacement, whereas the blue rim was left mostly intact. The analysed tourmalines have been classified as elbaites with elevated amounts of Cu, Mn and Zn, hence falling in the category of the “Paraíba-type”. The highest amounts of Cu (up to 2.3 wt.-%), have been detected in blue tourmaline samples. Turquoise crystals contain, in addition to their elevated Cu- content, high amounts of Mn (up to 2.5 wt.-%). Moreover, up to 2.4 wt.-% Zn was registered. Pink colours are due to a dominance in Mn and a depletion in Cu and Zn compared to the other samples as previously described by Beurlen et al. (2011). The green tourmaline species receive their colour by enhanced Fe-contents (up to 0.8 wt.-%) in combination with high amounts of Mn (up to >2 wt.-%) and medium Cu-concentrations (up to 0.4 wt.-%). The typical blueish-green, greenish-blue and “neon-blue” hues are seen as a consequence Cu- and Mn-abundance, which has been discussed extensively in previous publications (e.g. Okrusch et al., 2016; Perretti et al., 2009 and references therein). The analysed tourmalines display a blueish shade of green and contain both Mn as well as high amounts of Cu like the blue samples and elevated amounts of Fe, analogous to the green samples. The investigated samples are not clearly distinguishable from material origi– nating from other areas from Brazil (such as Paraíba-state), however, there is a clear difference in trace elements towards Paraíba-type tourmalines from Nigeria (which have higher Ga-, Ge- and Pb-concentrations) and Mozambique (elevated Be, Sc, Ga, Pb and Bi contents).
... Years after the initial discovery in the state of Paraíba, similar gem-quality elbaite tourmalines colored by copper and manganese were found elsewhere in Brazil (Shigley et al., 2001;Furuya, 2007), in Nigeria (Smith et al., 2001), and in Mozambique (Abduriyim and Kitawaki, 2005;Laurs et al., 2008). The composition of cuprian tourmaline from all of these deposits has been determined with energy-dispersive X-ray fluorescence spectrometry (EDXRF), electron microprobe analysis, and laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS; see Abduriyim et al., 2006;Okrusch et al., 2016). No mineral species other than elbaite has been previously reported for "Paraíba" tourmalines except for four pieces of Cu-bearing liddicoatite first reported by Karampelas and Klemm (2010) showing Ca-rich X-site occupancy and three ...
... Other liddicoatite tourmalines from Canada (Teertstra et al., 1999) have similar sodium (0.365- Table 3 shows the samples' averaged chemical composition for selected minor and trace elements. In cuprian tourmalines from different origins, these have some distinguishable trends (Abduriyim et al., 2006;Okrusch et al., 2016). For example, Brazilian and Nigerian cuprian tourmalines tend to show higher concentrations of Cu than those from Mozambique-which typically have higher Ga than the other two sources. ...
Chapter
Silicate minerals, including quartz, play a pivotal role in the make-up of planet Earth.