Crystal‑chemical behavior of Fe2+ in tourmaline dictated by structural stability: insights from a schorl with formula NaY(Fe2+2Al)Z(Al5Fe2+)(Si6O18)(BO3)3(OH)3(OH,F) from Seagull batholith (Yukon Territory, Canada)
| Autor: | Luca Samuele Capizzi, Ferdinando Bosi, Giovanni B. Andreozzi, Christopher E. Beckett-Brown, Vincenzo Stagno, Beatrice Celata |
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| Předmět: |
schorl
010504 meteorology & atmospheric sciences Tourmaline Chemistry Laser ablation inductively coupled plasma mass spectrometry tourmailne Electron microprobe 010502 geochemistry & geophysics single-crystal x-ray diffraction electron microprobe 01 natural sciences Bond length Crystal Crystallography Geochemistry and Petrology Batholith Structural stability Mössbauer spectroscopy General Materials Science 0105 earth and related environmental sciences |
| Zdroj: | Sapienza Università di Roma-IRIS |
| Popis: | A black tourmaline sample from Seagull batholith (Yukon Territory, Canada) was established to be a schorl with concentrations of Fe2+ among the highest currently found in nature (FeOtot ~ 18 wt.% and Fe2+ ~ 100% of Fetot) on the basis of a multi-analytical characterization through Mossbauer spectroscopy, electron microprobe, Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometry and single-crystal X-ray diffraction. From the crystal-chemical analysis, the following empirical formula is proposed: X(Na0.74□0.24K0.01Ca0.01)Σ1.00Y(Fe2+2.05Al0.92Ti0.02Mn0.01Zn0.01)Σ3.00Z(Al5.41Fe2+0.53Mg0.06)Σ6.00(Si6O18)(BO3)3V(OH)3W[(OH)0.46F0.41O0.13]Σ1.00, which can be approximated as NaY(Fe2+2Al)Z(Al5Fe2+)(Si6O18)(BO3)3(OH)3(OH,F). Compared to the formula of the ideal ordered schorl, NaY(Fe2+3)Z(Al6)(Si6O18)(BO3)3(OH)3(OH), the studied sample has a partial disorder of Fe2+ across the Y and the Z sites that can be expressed by the intracrystalline order–disorder reaction YAl + ZFe2+ → YFe2+ + ZAl. Such a partial cation disorder must be invoked to explain tourmaline structural stability because an ideal ordered schorl results in a large misfit between the and mean bond lengths (that is, between the YO6 and ZO6 polyhedra). This misfit is reduced by introducing Al at Y (i.e., through the shortening) and Fe2+ at Z (i.e., through the lengthening). The result is that in tourmaline the site distribution of high Fe2+ concentrations is dictated by long-range structural constraints. |
| Databáze: | OpenAIRE |
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