Publication Date:
2016-09-29
Description:
Vesuvianite containing 5.85 wt% TiO2from an Alpine-cleft-type assemblage outcropped near Alchuri, Shigar Valley, Northern Areas, has been investigated by means of electron microprobe analyses, gas-chromatographic analysis of H2O, X-ray powder diffraction, single-crystal X-ray structure refinement,27Al NMR,57Fe Mössbauer spectroscopy, IR spectroscopy and optical measurements. Tetragonal unit-cell parameters are:a= 15.5326 (2),c= 11.8040 (2) Å, space groupP4/nnc. The structure was refined to finalR1= 0.031,wR2= 0.057 for 11247I〉 2σ(I). A general crystal-chemical formula of studied sample can be written as follows (Z= 2):[8–9](Ca17.1Na0.9)[8]Ca1.0[5](Fe2+0.44Fe3+0.34Mg0.22)[6](Al3.59Mg0.41)[6](Al4.03Ti2.20Fe3+1.37Fe2+0.40) (Si18O68) [(OH)5.84O2.83F1.33]. The octahedral siteY2 is Al-dominant and does not contain transition elements. Another octahedral siteY3 is also Al-dominant and contains Fe2+, Fe3+and Ti. The siteY1 is split intoY1aandY1bpredominantly occupied by Fe2+and Fe3+, respectively. The role of theY1 site in the diversity of vesuvianite-group minerals is discussed.
Print ISSN:
2052-5192
Electronic ISSN:
2052-5206
Topics:
Chemistry and Pharmacology
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Geosciences
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Physics
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