Towards a revisitation of vesuvianite-group nomenclature: the crystal structure of Ti-rich vesuvianite from Alchuri, Shigar Valley, Pakistan

• Published in: Acta crystallographica Section B, Structural science, crystal engineering and materials Structural science, crystal engineering and materials, 2016-10, Vol.72 (5), p.744-752
• Main 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.
• Format: Article
• Language: English
• Subjects: 27Al NMR NMR spectroscopy; Chromatography, Gas; crystal chemistry; Crystal structure; Crystallography; Crystallography, X-Ray; IR spectroscopy; Iron - chemistry; Magnetic Resonance Spectroscopy; Minerals; Minerals - analysis; Minerals - chemistry; Mössbauer spectroscopy; Pakistan; Powders - chemistry; Spectrophotometry, Infrared; Spectroscopy, Mossbauer; Titanium - chemistry; vesuvianite; X-Ray Diffraction
• ISSN: 2052-5206; 2052-5192; 2052-5206
• DOI: 10.1107/S2052520616010246

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 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 group P4/nnc. The structure was refined to final R1 = 0.031, wR2 = 0.057 for 11247 I > 2σ(I). A general crystal‐chemical formula of studied sample can be written as follows (Z = 2): [8–9](Ca17.1Na0.9) [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 site Y2 is Al‐dominant and does not contain transition elements. Another octahedral site Y3 is also Al‐dominant and contains Fe2+, Fe3+ and Ti. The site Y1 is split into Y1a and Y1b predominantly occupied by Fe2+ and Fe3+, respectively. The role of the Y1 site in the diversity of vesuvianite‐group minerals is discussed. 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 Y1 site in the diversity of vesuvianite‐group minerals is discussed.