Tetrahedrally coordinated boron in tourmalines from the liddicoatite-elbaite series from Madagascar: Structure, chemistry, and infrared spectroscopic studies
-
Andreas Ertl
,
John M. Hughes
Abstract
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.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Presidential Address to the Mineralogical Society of America, Salt Lake City, October 18, 2005: Mineral surfaces and the prebiotic selection and organization of biomolecules
- A rare garnet-tourmaline-sillimanite-biotite-ilmenite-quartz assemblage from the granulite-facies region of south-central Massachusetts
- Effects of natural radiation damage on back-scattered electron images of single crystals of minerals
- Thermal diffusivity of olivine-group minerals at high temperature
- Quantum mechanical vs. empirical potential modeling of uranium dioxide (UO2) surfaces: (111), (110), and (100)
- AXANES study of Cu speciation in high-temperature brines using synthetic fluid inclusions
- A new approach to determine and quantify structural units in silicate glasses using micro-reflectance Fourier-Transform infrared spectroscopy
- Titanium incorporation and VITi3+ -IVTi4+ charge transfer in synthetic diopside
- Hugoniot and impact-induced phase transition of magnesite
- Finite element modeling of elastic volume changes in fluid inclusions: Comparison with experiment
- Thermodynamics of mixing in pyrope-grossular, Mg3Al2Si3O12-Ca3Al2Si3O12, solid solution from lattice dynamics calculations and Monte Carlo simulations
- Does antigorite really contain 4- and 8-membered rings of tetrahedra?
- New insight into crystal chemistry of topaz: A multi-methodological study
- Tetrahedrally coordinated boron in tourmalines from the liddicoatite-elbaite series from Madagascar: Structure, chemistry, and infrared spectroscopic studies
- Recovery of stishovite-structure at ambient conditions out of shock-generated amorphous silica
- New experimental data on biotite + magnetite + sanidine saturated phonolitic melts and application to the estimation of magmatic water fugacity
- Structural effects of pressure on triclinic chlorite: A single-crystal study
- New high-pressure phase relations in CaSnO3
- A high-pressure Raman spectroscopic study of hafnon, HfSiO4
- Single-crystal elasticity of brucite, Mg(OH)2, to 15 GPa by Brillouin scattering
- The effect of composition on Cr2+/Cr3+ in silicate melts
- Phosphohedyphane, Ca2Pb3(PO4)3Cl, the phosphate analog of hedyphane: Description and crystal structure
- Synthesis of novel leadmolybdenum and leadtungsten oxyhalides with the pinalite structure, Pb3MoO5Cl2 and Pb3WO5Br2
- Depolymerization effect of water in aluminosilicate glasses: Direct evidence from 1H-27Al heteronuclear correlation NMR
- Hydroxylellestadite from Cioclovina Cave (Romania): Microanalytical, structural, and vibrational spectroscopy data
- Matioliite, the Mg-analog of burangaite, from Gentil mine, Mendes Pimentel, Minas Gerais, Brazil, and other occurrences
- Letter. Crystallographic alignments in a coccolith (Pleurochrysis carterae) revealed by electron back-scattered diffraction (EBSD)
- Letter. High-pressure study of FeS, between 20 and 120 GPa, using synchrotron X-ray powder diffraction
