Mn-bearing purplish-red tourmaline from the Anjanabonoina pegmatite, Madagascar
| Autor: | Henrik Skogby, Erica Bittarello, Beatrice Celata, Alessandra Marengo, Gioacchino Tempesta, Marco E. Ciriotti, Ulf Hålenius, Ferdinando Bosi |
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| Rok vydání: | 2021 |
| Předmět: |
010504 meteorology & atmospheric sciences
Tourmaline Absorption spectroscopy purplish-red tourmaline Infrared spectroscopy Electron microprobe engineering.material laser induced breakdown spectroscopy 010502 geochemistry & geophysics 01 natural sciences crystal-structure refinement electron microprobe infrared spectroscopy optical absorption spectroscopy Raman spectroscopy symbols.namesake Geochemistry and Petrology Elbaite Pegmatite 0105 earth and related environmental sciences Mineral Chemistry Geokemi Crystallography Geochemistry engineering symbols |
| Zdroj: | Mineralogical Magazine. 85:242-253 |
| ISSN: | 1471-8022 0026-461X |
| DOI: | 10.1180/mgm.2021.20 |
| Popis: | A gem-quality purplish-red tourmaline sample of alleged liddicoatitic composition from the Anjanabonoina pegmatite, Madagascar, has been fully characterised using a multi-analytical approach to define its crystal-chemical identity. Single-crystal X-ray diffraction, chemical and spectroscopic analysis resulted in the formula: X(Na0.41□0.35Ca0.24)Σ1.00Y(Al1.81Li1.00Fe3+0.04Mn3+0.02Mn2+0.12Ti0.004)Σ3.00ZAl6 [T(Si5.60B0.40)Σ6.00O18] (BO3)3 (OH)3W[(OH)0.50F0.13O0.37]Σ1.00 which corresponds to the tourmaline species elbaite having the typical space group R3m and relatively small unit-cell dimensions, a = 15.7935(4) Å, c = 7.0860(2) Å and V = 7.0860(2) Å3.Optical absorption spectroscopy showed that the purplish-red colour is caused by minor amounts of Mn3+ (Mn2O3 = 0.20 wt.%). Thermal treatment in air up to 750°C strongly intensified the colour of the sample due to the oxidation of all Mn2+ to Mn3+ (Mn2O3 up to 1.21 wt.%). Based on infrared and Raman data, a crystal-chemical model regarding the electrostatic interaction between the X cation and W anion, and involving the Y cations as well, is proposed to explain the absence or rarity of the mineral species ‘liddicoatite’. |
| Databáze: | OpenAIRE |
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