Tourmaline Samples Research Articles

Determination of Tourmaline Composition in Pegmatite From Buldan, Denizli (Western Anatolia, Turkey) Using XRD, XRF, and Confocal Raman Spectroscopy

ABSTRACT Tourmaline minerals observed in different geologic environments show significant variations in terms of chemical compositions. Determination of tourmaline species gives useful petrogenetic information about both igneous and metamorphic environments. Microscopic, XRD, XRF, and confocal Raman spectroscopic features of tourmaline segregations that are 2–4 cm thick, dark-blue to black in color, and mostly fractured occurring in the Buldan pegmatite are reported. Under the microscope, tourmaline samples show indigo blue, light blue, and olive-brown pleochroism with a thin long columnar, bladed shape. They exhibit distinctive enrichments in Fe2O3 (7.83–10.16 wt%), V (245.0–591.0 ppm), Sn (70.1–147.3 ppm), W (1076.0–1887.0 ppm), U (1.2–18.2 ppm), and Th (9.6–28.0 ppm). In terms of geochemistry, the tourmaline samples are schorl with Fe/(Fe + Mg) ratios of 0.65–0.74 and Na/(Na + Ca) ratios of 0.88–0.93. Five characteristic bands of tourmaline samples are observed at 1050, 710, 370, 220–245, and 185 cm−1. Tourmaline segregations in the Buldan pegmatite are schorl in composition and are probably generated from Li-poor granitoids and their associated pegmatites.

Extraction and Determination of Boron Isotopic Composition in Tourmalines

Tourmaline is an abundant boron-rich alumosilicate mineral with complex chemistry and rich in Fe, Mg, Al, Si elements. In this study, tourmaline samples were decomposed by alkali fusion method, and then the boron was separated and purified using three different procedures. It was found that both Fe3+ and Al3+ ions, rich in tourmaline samples seriously, which affected the accurate determination of boron concentration by Azomethine-H spectrophotometric method and also caused a loss of boron by specific adsorption when large amount of amorphous hydroxide precipitate formed in ion-exchange columns. The addition of small amount of EDTA can eliminate the influence, but brings serious isobaric interference on boron isotopic analysis by TIMS. Finally, a three-column ion-exchange procedure was established including the first mixed resin column, the peristaltic pump coupled boron specific resin column, and the second mixed resin column, which ensures the full recovery of boron (> 99%) from tourmaline samples with complex matrices. The PTIMS-Cs2BO2+-static double-collection method was established by selecting H3-H4 Faraday cups and optimizing parameters in Zoom Optics (Focus Quad: 15; Dispersion Quad: −85) in a Triton TI mass spectrometer. The determined average 11B/10B value of NIST SRM 951 standard boron solution was 4.05044±0.00012 (2σ, n = 8, 1 μg B), which was superior to the dynamic collection method in internal/external precision. A δ11B value of −0.3% for NIST SRM 951 through the same pretreatment procedure was obtained, indicating that there was no isotopic fractionation occurred during the extraction procedure. The comparison of boron isotopic compositions in natural samples by TIMS and MC-ICP-MS after the chemistry procedure indicated that δ11B values determined by the static PTIMS-Cs2BO2+ method were in good agreement with that by MC-ICP-MS.

The [9]-coordinatedXsite in the crystal structure of tourmaline-group minerals

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 Al6 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 ∼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 Al6 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.

Colorimetry Study on Red Tourmaline Color Genesis

In this paper, the colorimetry characteristics of ten red tourmaline samples were studied through the visible light spectrometer Color I5 of X-rite company of the United States. In order to give a quantitative description of the color of red tourmalines, the chromaticity index of the samples was measured, and the red tourmaline color parameters with possible principle and technology for evaluation were obtained, including chroma coordinates, main wavelength, chroma, brightness, curves of reflection rate and chroma figures. Combining with the electron probe microanalysis and the chemical analysis, the relationship between the content change of color-caused ions and the color parameters was discussed by analyzing the existing states and content of color-caused ions Mn2+(ion), Cr3+(ion) and Fe2+(ion).

Iron redox reactions in the tourmaline structure: High-temperature treatment of Fe3+-rich schorl

We present a detailed study of thermally-driven oxidation and reduction of Fe in the structure of schorl (as the most widespread tourmaline), Fe2+-bearing olenite and fluor-schorl. The principal Fe3+-rich tourmaline investigated in this study is a natural schorl sample from a unique occurrence in peralkaline rocks near Cancrinite Hill, east of Bancroft, southern Ontario. Tourmaline samples were thermally-treated in air and hydrogen at temperatures of 700, 800 and 900°C to oxidize or reduce the structural Fe. High-temperature changes were continuously monitored using 57Fe Mössbauer and infrared spectroscopy. Proportions of Fe2+ and Fe3+ vary as a function of the heat treatment. An increase in Fe3+ up to 100% after heating in air at 700°C was observed, whereas only small changes in the Fe3+/Fetot ratio after heating under hydrogen at 700°C was revealed. Partial deprotonation/protonation represents charge compensation for the oxidation/reduction of Fe at the Y and Z sites.Critical samples of Cancrinite Hill tourmaline were investigated in detail by means of 57Fe Mössbauer and infrared spectroscopy, single-crystal X-ray diffraction, electron microprobe and magnetometry. The optimized structural formulae are:X(Na0.93K0.02□0.05)Y(Ti0.13Al0.20Fe1.263+Fe1.102+Mn0.022+□0.30)Z(Al5.16Fe0.532+Mg0.31)BB3T(Si5.88Al0.12)O27V(OH)3W(O0.12OH0.88) – untreated tourmaline (schorl);X(Na0.93K0.02□0.05)Y(Ti0.13Al0.52Fe1.143+Fe0.842+Mg0.05Mn0.022+□0.30)Z(Al4.85Fe0.902+Mg0.25)BB3T(Si5.88Al0.12)O27V(OH)3W(OH) – tourmaline reduced in hydrogen (schorl);X(Na0.93K0.02□0.05)Y(Ti0.13Al0.40Fe2.003+Mg0.15Mn0.022+□0.30)Z(Al4.99Fe0.873+Mg0.14)BB3T(Si5.90Al0.10)O27V(O1.05OH1.95)W(O0.70OH0.30) – tourmaline oxidized in air (H+-rich “buergerite”).There is evident disorder of Al over the Y, Z and T sites as well as disorder of Fe2+ over the Y and Z sites, and ordering of Fe3+ at the Y site and Mg at the Z site. The fully oxidized tourmaline shows disorder of Fe3+ and Mg over the Y and Z sites. The occurrence of “extra” Fe2+ in the Z site of the reduced tourmaline relative to the untreated sample demonstrates the intracrystalline cation-exchange YR2++ZR3+⇆YR3++ZR2+ driven by elevated temperature. Increased disorder of Fe cations over the edge-shared YO6 and ZO6 octahedra enhances the antiferromagnetic exchange interactions in the tourmaline structure, which are stronger in reduced samples than in oxidized and untreated ones. This suggests that OH groups at the W site could mediate Y–Z inter-site exchange interactions.Complete oxidation of Fe within the tourmaline structure is possible. However, significant reduction of Fe cannot occur because an excess of H+ may not be incorporated within the tourmaline structure. Further reduction of Fe3+ will not occur until the breakdown of the tourmaline structure above its temperature of reductive decomposition, where metallic Fe immediately appears as a separate phase (α-Fe) together with cristobalite and Na–Al–Fe-borosilicate glass. The scarcity of Fe3+-rich tourmalines in nature and the separate existence of “buergerite” as the only tourmaline with almost all Fe as Fe3+ support its specific origin, such as from an HT-LP, high fO2 overprint.

Testing Method of Infrared Emissivity Used in Powders Industry

The test apparatus of infrared emissivity used in powders industry was researched by controlling the temperature accurately and collecting the signals of surface temperature of two standard samples and a test sample. The tourmaline samples from ten mines had been tested by the new test apparatus. Compared with the results from FTIR, it was shown that average value of relative error was 0.378% and repeatability error was less than 0.6% after correcting by the coefficient kc = 0.958.

Testing Method of Spontaneous Polarity Used in Powders Industry

By fitting calculation of functional relationship between charge quantity and temperature on condition that powders were shielded, a device was proposed to measure spontaneous polarity of powders, and samples of typical tourmaline were measured. The results showed when tourmaline powders of different origins were heated to 80, minimum value of spontaneous polarization strength was 3.204×10-4C/m2, and maximum value was 1.53×10-3C/m2. The conclusion was in accord with results got from crystal structure analysis, and repeatability r was 1.726×10-6C/m2with 95% confidence probability.

Crystallochemical effects of heat treatment on Fe-dominant tourmalines from Dolní Bory (Czech Republic) and Vlachovo (Slovakia)

Heat treatment was performed on selected Fe-dominant tourmalines to establish the nature of any change in optical properties. Two tourmaline samples from Dolni Bory, Czech Republic (TDB) and Vlachovo, Slovakia (TVL) were heated at 450, 700 and 900°C at 0.1 mPa and ambient oxidation conditions for 8 h. EMPA study shows that tourmaline from Vlachovo has schorlitic composition and tourmaline from Dolni Bory is alkali-depleted schorl to foitite. Although the black colour remained unchanged after heating at 450°C, it changed to brown at 700°C and reddish brown at 900°C. No significant changes of chemical composition were observed during heating. X-ray diffraction, infrared and Mossbauer study showed negligible oxidation of tourmaline heated at 450°C, but a significant change in iron valency state and deprotonization at 700°C. The oxidation of Fe is the main cause of tourmaline colour change, and the substitution vector for oxidation of Fe is Fe3+OFe−12+(OH)−1. The predicted deprotonization of OH was confirmed by infrared spectroscopy, which documented a decrease in OH groups in both samples, mainly at the V site. The oxidation of Fe is mostly significant in the Y site as documented on the compression of the Y-site octahedra and subsequent decrease in the a lattice parameter. This feature is consistent with lattice dimensions in the transition from schorl and foitite dimensions to those consistent with fluor-buergerite. The Z-site octahedra did not compressed and were not affected by heating-induced Fe oxidation, which indicates only negligible content of ZFe2+ in original samples. After heating at 900°C, the tourmaline structure collapsed likely due to the thermally induced weakening of bonds in Y and Z octahedra, which results in amorphization of tourmaline. Subsequently, breakdown products including Fe-oxides and mullite replaced alkali-depleted amorphized tourmaline.

Li-bearing, disordered Mg-rich tourmaline from a pegmatite-marble contact in the Austroalpine basement units (Styria, Austria)

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 0.29 wt% Li2O, and can be characterized as dravite, with FeO contents of ~ 0.9–2.7 wt%. 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) A 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) A, 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 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 (~8–36 ppm) and Th (0.1–1.8 ppm) 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.

Non-integral hybrid ions in tourmaline: buffering and geo-thermometry

The tourmaline group of minerals is indeed an enigma. Experimental data from optical spectroscopy, electron microscopy, and Mossbauer spectroscopy reveal a host of physical properties that lack a common structural clarification. For example, tourmaline samples change colour when irradiated with X-ray and gamma-ray radiations some reverting back when heated in air; exhibit simultaneous oxidation and reduction on annealing in an atmosphere of H-2; display different plane group symmetries under TEM; possess the most complicated Mossbauer spectra of all Fe-bearing silicates. In this study, four Brazilian samples were chosen for detailed study by Mossbauer spectroscopy to find out a common structural factor to the physical anomalies reported in the literature. It was found out that the tourmaline group of minerals contain multi-valence elements that are involved in electron exchange between the edge-sharing asymmetric Y and Z crystallographic sites. It is conceivable that the host of physical properties recorded in the literature could be due to the inherent structural misfit between the Y and Z sites and the mechanisms adopted to reduce the strain associated along the shared edges. The complexity of non-integral oxidation states possible - due to electron sharing among the different multi-valence elements present in the structure - further enhances the diverse physical properties observed. Moreover, on heating in air, no net oxidation or reduction takes place in the tourmaline group of minerals over a temperature range as long as there are electron donors and acceptors left in the structure, serving simultaneously as potential single-phase buffers and geo-thermometers.

Mushroom elbaite from the Kat Chay mine, Momeik, near Mogok, Myanmar: I. Crystal chemistry by SREF, EMPA, MAS NMR and Mössbauer spectroscopy

AbstractTourmaline from the Kat Chay mine, Momeik, near Mogok, Shan state, Myanmar, shows a variety of habits that resemble mushrooms, and it is commonly referred to as ‘mushroom tourmaline'. The structure of nine single crystals of elbaite, ranging in colour from pink to white to black and purple, extracted from two samples of mushroom tourmaline from Mogok, have been refined (SREF) to R indices of ~2.5% using graphite-monochromated Mo-Kα X-radiation. 11B and 27Al Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy shows the presence of [4]B and the absence of [4]Al in samples with transition-metal content low enough to prevent paramagnetic quenching of the signal. Site populations were assigned from refined site-scattering values and unit formulae derived from electron-microprobe analyses of the crystals used for X-ray data collection. 57Fe Mössbauer spectroscopy shows that both Fe2+ and Fe3+ are present, and the site populations derived by structure refinement show that there is no Fe at the Z site; hence all Fe2+ and Fe3+ occurs at the Y site. The 57Fe Mössbauer spectra also show peaks due to intervalence charge-transfer involving Fe2+ and Fe3+ at adjacent Y sites. Calculation of the probability of the total amount of Fe occurring as Fe2+–Fe3+ pairs for a random short-range distribution is in close accord with the observed amount of Fe involved in Fe2+–Fe3+, indicating that there is no short-range order involving Fe2+ and Fe3+ in these tourmalines.

The Ti-influence on the tourmaline color

Titanium was examined in different black tourmalines by spectrophotometric analyses in the region between 12500 and 27000 cm-1 (800-370 nm) using a microscope spectrophotometer MPV-5P, Leitz (Germany), and chemically analyzed on an electron microprobe Camebax Microbeam, Cameca (France) in WDS Mode. Fourteen tourmaline samples with their face oriented parallel to the principal axis, cut and polished down to thin sections, showed polarized spectra of two broad absorption bands at approximately 14000 cm-1 (715 nm) and 24000 cm-1 (417 nm). Precision thickness measurements were used to calculate the absorption coefficients α. For the absorption around 24000 cm-1, a linear correlation was observed between α and the TiO2 content (mass %). Another linear regression was observed between α and the product of TiO2 and FeO (%) contents. Cations located in the Y- and Z-octahedrons of the structure that are connected over edges might contribute to intervalence charge transfer transitions (IVCT) between Ti3+-Ti4+, Fe2+-Ti4+ and Ti3+-Ti4+-Fe3+.

Tetrahedrally coordinated boron in tourmalines from the liddicoatite-elbaite series from Madagascar: Structure, chemistry, and infrared spectroscopic studies

Four colorless tourmalines of the liddicoatite-elbaite series from pegmatites from Anjanabonoina, Madagascar, have been characterized by crystal-structure determination and by chemical analyses. Optimized formulae range from X(Ca0.57Na0.29□0.14) Y(Al1.41Li1.33Mn2+0.07□0.19) ZAl6T(Si5.86B0.14)O18 (BO3)3V(OH)3.00W[F0.76(OH)0.24] [a = 15.8322(3), c = 7.1034(3) Å] to X(Na0.46Ca0.30□0.24) Y(Al1.82Li0.89Fe2+0.01 Mn2+0.01□0.27) ZAl6T(Si5.56B0.44)O18 (BO3)3V(OH)3.00W[(OH)0.50F0.50] [a = 15.8095(9), c = 7.0941(8) Å] (R = 1.3.1.7%). There is a high negative correlation (r2 = 0.984) between the <T-O> bond-lengths (~1.618.1.614 Å) and the amount of IVB (from the optimized formulae). Similar to the olenites (from Koralpe, Austria) the liddicoatite-elbaite samples show a positive correlation between the Al occupancy at the Y site and IVB (r2 = 0.988). Short-range order configurations show that the presence of IVB is coupled with the occupancy of (Al2Li) and (Al2□) at the Y site. The structural formulae of the Al-rich tourmalines from Anjanabonoina, Madagascar, show ~ ⃞0.2 (vacancies) on the Y site. We believe that short-range order configurations with Y(Al2□) are responsible for these vacancies. Hence, an oft-used calculation of the Li content by difference on the Y site may be problematic for Al-rich tourmalines (olenite, elbaite, rossmanite). Fourier transform infrared (FTIR) spectra were recorded from the most IVB-rich tourmaline sample. The bands around 5195 and 5380 cm-1 can be assigned to H2O. Because these bands still could be observed in FTIR spectra at temperatures from -150 to +600 °C, it seems unlikely that they result from H2O in fluid inclusions. Interestingly, another FTIR spectrum from a dravite in which the X site is filled completely with Na, does not show bands at ~5200 and ~5400 cm-1. Although not definitive, the resulting spectra are consistent with small amounts of H2O at the X site of the elbaite. The rare-earth element (REE) pattern of the B-rich elbaite (ΣREE: ~150 ppm) demonstrates that this sample is strongly enriched in LREEs compared to HREEs and exhibits a negative Eu anomaly. This sample shows the strongest enrichment of LREEs and a high LaN/YbN ratio of ~351, which seems to confirm an important role of the fractional crystallization process.

Effect of heat treatment on tourmaline from Brazil

The crystal-chemical behaviour of tourmaline from Aracuai, Minas Gerais state, Brazil, when subjected to heating in air atmosphere has been studied by several techniques, including EMPA, UV–Vis, TGA, and Mossbauer spectroscopy. The tourmaline samples are typically intermediate members of the elbaite-schorl series. The origin of colour and of its change after treatment has been discussed in terms of local disorder, presence of metal transition elements, oxidation of ferrous iron at the octahedral site, and simultaneous trap of the excess electron. These findings may be used to enhance the colour in tourmaline crystals or generate wanted colour changes.

Mn-bearing "oxy-rossmanite" with tetrahedrally coordinated Al and B from Austria: Structure, chemistry, and infrared and optical spectroscopic study

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(⃞ 0.53Na0.46Ca0.01) Y(Al2.37Li0.33Mn2+0.25Fe2+0.04Ti4+0.01) ZAl6T(Si5.47Al0.28B0.25)O18 (BO3)3 V[(OH)2.85O0.15] W[O0.86(OH)0.10F0.04], with a = 15.8031(3), c = 7.0877(3) Å, and R = 0.017 for the sample with 2.05 wt% MnO, and X(⃞0.53Na0.46Ca0.01) Y(Al2.35Li0.32Mn2+0.28 Fe2+0.04Ti4+0.01) ZAl6T(Si5.51Al0.25B0.24)O18 (BO3)3V[(OH)2.80O0.20] W[O0.86(OH)0.10F0.04] for a sample with a = 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 <T-O> bond-lengths (~1.620 Å) mask the incorporation of [4]B because of the incorporation of [4]Al. The <T-O> 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% Al2O3; ~8.6 apfu Al). The nearinfrared 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 (σoct2) of the ZO6 octahedron and the <Y-O> distance. On a bond-angle distortion-<Y-O> 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 Mn3+ produced by natural irradiation of Mn2+. 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”.

The spectrophotometric determination of boron in tourmalines

A procedure for the spectrophotometric determination of macro amounts of boron in tourmaline with azomethine H is described. The used tourmaline concentrate was obtained by magnetic separation and heavy-liquids purification of the schorl zone of pegmatite or granite aplite. The samples of tourmaline were decomposed by fusion with anhydrous sodium carbonate and taken up in dilute hydrochloric acid. The interfering effects of iron and aluminium were eliminated by masking with an EDTA - NTA solution. After pH adjustment, the boron was reacted with azomethine H and the absorbance of the obtained coloured complex was measured at 415 nm. The results are compared with those obtained by other procedures. The relative error of the determination was less than 3 %.

Crystal-chemical characterization of tourmalines from the English Lake District: Electron-microprobe analyses and Mössbauer spectroscopy

Electron-microprobe analyses (EMPA) and Mössbauer spectra (MS) have been acquired for natural tourmalines sampled near Crummock Water and Haweswater, English Lake District. In the former, the dravite-schorl series is prevalent, whereas in the latter, the dravite species is dominant. All tourmaline samples presently studied are chemically disordered. The compositional and MS data give an insight into the thermal and fluid evolution experienced by the tourmalinite rocks. The tourmalines from Crummock Water crystallized in a closed, low fO₂ environment, under the influence of a magmatic fluid. The tourmalines from Haweswater are of hydrothermal origin and were formed under low, variable T and low fO₂ conditions, from a fluid of constant composition.

Metamorphic Na- and OH-rich disordered dravite with tetrahedral boron, associated with omphacite, from Syros, Greece: chemistry and structure

Metamorphic Fe-bearing dravite from a glaucophane schist from Syros, Greece, associated with omphacite, has been characterized by chemical analyses (EMPA, SIMS, Mossbauer study) and by crystal structure determination. The optimized formula, calculated using chemical and structural data (including from Mossbauer spectroscopy) is x (Na 0.96 Ca 0.02 □ 0.02 ) Y (Mg 1.29 Al 0.99 Fe 2+ 0.44 Fe 3+ 0.19 Ti 0.05□ 0.04 ) Z (Al 4.90 Mg 1.10 ) T (Si 5.83 B 0.17 ) B 3 O 27 [(OH) 3.93 F 0.07 ], with a = 15.9443(3), c = 7.2094(3) A, R = 0.017. The OH- content is nearly 4 apfu , thus there is no significant O 2− at the V and W site. The X site is nearly completely filled with Na, contrary to most natural tourmalines. We conclude that tourmaline samples from the dravite-schorl series where the O1 site ( W site) is mainly occupied by OH- and/or F, but not by O 2− , favour an X -site occupation with Na. Mg and Al are strongly disordered in this tourmaline sample. This Mg-rich tourmaline is an unusual example of Al-Mg disorder which is not driven by the short-range requirements of O 2− at the O 1 site. Surprisingly, we found small amounts of [4] B in this Mg-rich dravite. This is confirmed by the chemical analysis (including light elements), by the refinement (∼ 0.26 [4] B apfu ), as well as by the relatively small T -O> distance of 1.6179 A. This is the first known example of a Mg-rich tourmaline which contains significant amounts of [4] B. The formation of this dravite (at PT conditions of ∼ 6 to 7 kbar/∼ 400°C) took place in a subduction-exhumation environment at undersaturated SiO 2 -conditions.

Crystal chemistry of the schorl-dravite series

Nineteen tourmaline samples of various provenances and geological settings were studied by EMPA, SREF and MS to represent the schorl-dravite compositional field. All samples belong to the Alkali group (except one with an X -site vacancy content of 0.53 apfu) and to the Oxy- and Hydroxy-subgroups. Among divalent cations, the main substitution involves Y Mg for Y Fe 2+ , to produce the two end-members dravite and schorl. Site populations were determined by a new minimization procedure that simultaneously accounts for both structural and chemical data. Results show that the crystals are characterized by disordered cation distribution between Y and Z sites: Al populates both sites, with a marked preference for the smaller Z octahedron; Mg is often equally distributed between Y and Z . Both Fe 2+ and Fe 3+ populate both Y and Z sites, but show a strong preference for Y . Specific mean bond distances (A) optimised for major elements are: Y Al-O = 1.908, Y Mg-O = 2.084, Y Fe 2+ -O = 2.139, z Al-O = 1.900, z Mg-O = 2.077 and z Fe 2+ -O = 2.131. In the schorl-dravite solid solution, structural variations appear to be primarily due to Y and Z interactions. These effects are conspicuous over the entire structure, as Y dimensions directly affect the a cell parameter, while Z is similarly correlated with c. The dimensions of Y and Z octahedra are determined by Al contents. Dimensional variations of Z are well described by its bond-distance variations, except for Z -07D. Both octahedra reciprocally interact, influencing their distortions: inverse correlations exist between Y dimension vs. Z quadratic elongation and Z dimension vs. Y quadratic elongation. As a common feature, the effects of the octahedral second coordination sphere are only confined to polyhedral distortions instead of dimensional variations, which only depend on site populations.

Experts de la Revue de M�decine Interne sollicit�s en 2003

Understanding hydrothermal fluid flow events related to orogenic events is important because they provide large-scale redistribution of metals which may become concentrated in ore deposits. In this study we determine the origin of tourmaline-bearing quartz veins and pegmatites in the Western fold belt of the Proterozoic Mount Isa inlier, a region which host numerous syn-orogenic Cu deposits. This paper uses tourmaline mineral chemistry and isotopic analyses (in-situ B and bulk O and H isotopes) to fingerprint the fluid reservoirs that contributed to the fluid budget during the Isan orogeny. All the tourmaline samples have schorl–dravite solid solution compositions. Quartz–tourmaline δ18O (11.0–12.6 and 7.7–9.4‰ V-SMOW, respectively) pairs yield equilibrium formation temperatures of 305 to 575 °C with the higher temperatures related to pegmatitic tourmaline. Tourmaline δD values have a relatively narrow range from − 68 to − 56‰ V-SMOW. In most cases calculated δ18OFluid and δDFluid values are compatible with primary magmatic water with a small component of metamorphic/18O-enriched formation waters. However, there are large variations in tourmaline δ11B values which range from + 10.7 to − 17.0‰, with the majority of values between − 10 and − 15‰. Variations in δ11BTur in the pegmatites suggest that boron degassing generated relative 11B depletion during crystallization. Similar δ11BTur values in quartz–tourmaline veins spatially associated with the pegmatites, in cordierite- and sillimanite-bearing metamorphic rocks west of the Mount Isa fault, demonstrate a similar origin for B in this tourmaline. In contrast, quartz–tourmaline veins of similar timing hosted by greenschist grade metamorphic rocks east of the Mount Isa fault have much higher δ11BTur values (+ 6.2 to + 10.7‰) which reflect the involvement of a distinct B isotopic reservoir; mostly likely a near-surface derived evaporitic brine. Thus, the B isotopic data reveal important differences in fluid origin that are not reflected in the δ18O values. Therefore, at least two isotopically distinct fluids, one sourced from fractionating anatectic pegmatites and the other from external basinal brines, circulated contemporaneously in separate areas during the Isan orogeny. There is no evidence, based on the tourmaline isotopic data, to suggest that these fluids mixed, which demonstrates that the hydrothermal plumbing system in the Western fold belt during the Isan orogeny was disconnected, probably due to differences in thermal structure/metamorphic grade across the Western fold belt during orogenesis.