Towards a revisitation of vesuvianite‐group nomenclature: the crystal structure of Ti‐rich vesuvianite from Alchuri, Shigar Valley, Pakistan. Issue 5 (3rd October 2016)

• Record Type: Journal Article
• Authors: Aksenov, Sergey M.; Chukanov, Nikita V.; Rusakov, Vyacheslav S.; Panikorovskii, Taras L.; Rastsvetaeva, Ramiza K.; Gainov, Ramil R.; Vagizov, Farit G.; Lyssenko, Konstantin A.; Belakovskiy, Dmitry I.
• Is Part Of: Acta crystallographica. Volume 72:Issue 5(2016:Oct.)
• Page Start: 744
• Page End: 752
• Publication Date: 2016-10-03
• Subjects: vesuvianite -- crystal chemistry -- 27Al NMR NMR spectroscopy -- Mössbauer spectroscopy -- IR spectroscopy
• DOI: 10.1107/S2052520616010246
• Languages: English
• ISSNs: 2052-5206

Abstract

Abstract : Vesuvianite containing 5.85 wt% TiO2 from an Alpine‐cleft‐type assemblage outcropped near Alchuri, Shigar Valley, Northern Areas, Pakistan, has been studied. The role of the Y 1 site in the diversity of vesuvianite‐group minerals is discussed. Abstract : Vesuvianite containing 5.85 wt% TiO2 from an Alpine‐cleft‐type assemblage outcropped near Alchuri, Shigar Valley, Northern Areas, Pakistan, has been investigated by means of electron microprobe analyses, gas‐chromatographic analysis of H2 O, X‐ray powder diffraction, single‐crystal X‐ray structure refinement, 27 Al NMR, 57 Fe Mössbauer spectroscopy, IR spectroscopy and optical measurements. Tetragonal unit‐cell parameters are: a = 15.5326 (2), c = 11.8040 (2) Å, space group P 4/ nnc . The structure was refined to final R 1 = 0.031, wR 2 = 0.057 for 11247 I > 2σ( I ). A general crystal‐chemical formula of studied sample can be written as follows ( Z = 2): [8–9] (Ca17.1 Na0.9 ) [8] Ca1.0 [5] (Fe 2+ 0.44 Fe 3+ 0.34 Mg0.22 ) [6] (Al3.59 Mg0.41 ) [6] (Al4.03 Ti2.20 Fe 3+ 1.37 Fe 2+ 0.40 ) (Si18 O68 ) [(OH)5.84 O2.83 F1.33 ]. The octahedral site Y 2 is Al‐dominant and does not contain transition elements. Another octahedral site Y 3 is also Al‐dominant and contains Fe 2+, Fe 3+ and Ti. The site Y 1 is split into Y 1 a and Y 1 b predominantly occupied by Fe 2+ and Fe 3+, respectively. The role of the Y 1 site in the diversity of vesuvianite‐group minerals is discussed.