IngentaConnect Kokchetavite: a new potassium-feldspar polymorph from the Kokchet...

Authors: Hwang, Shyh-Lung¹; Shen, Pouyan²; Chu, Hao-Tsu³; Yui, Tzen-Fu⁴; Liou, Juhn⁵; Sobolev, Nikolay⁶; Zhang, Ru-Yuan⁵; Shatsky, Vladislav⁶; Zayachkovsky, Anton⁷

Source: Contributions to Mineralogy and Petrology, Volume 148, Number 3, November 2004 , pp. 380-389(10)

Publisher: Springer

Abstract:

Kokchetavite, a new polymorph of K-feldspar (KAlSi₃O₈), has been identified as micrometer-size inclusions in clinopyroxene and garnet in a garnet-pyroxene rock from the Kokchetav ultrahigh-pressure terrane, Kazakhstan. Kokchetavite has a hexagonal structure with a =5.27(1) Å, c=7.82(1) Å, V=188.09 Å³, Z=1, and is found to be associated with phengite + α/β-cristobalite (or quartz) + siliceous glass ± phlogopite/titanite/calcite/zircon, occurring as multi-phase inclusions in clinopyroxene and garnet. It is concluded that kokchetavite could not be an exsolution phase in host minerals. Instead, it might be metastably precipitated from an infiltrated K-rich melt during rock exhumation. Alternatively, although less likely, kokchetavite might be derived from dehydration of K-cymrite, which, in turn, was formed at high pressures. In either case, kokchetavite is a metastable polymorph of K-feldspar.

Document Type: Research article

DOI: 10.1007/s00410-004-0610-2

Affiliations: 1: Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan, ROC, Email: slhwang@mail.ndhu.edu.tw 2: Institute of Materials Science and Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan, ROC, 3: Central Geological Survey, P.O. Box 968, Taipei, Taiwan, ROC, 4: Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, ROC, 5: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA, 94305, USA, 6: Institute of Mineralogy and Petrography, Siberian Branch of Russian Academy of Sciences, 630090, Novosibirsk, Russia, 7: NEDRA Geological Expedition, 475013, Kokchetav, Kazakhstan,

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Kokchetavite: a new potassium-feldspar polymorph from the Kokchetav ultrahigh-pressure terrane