Kokchetavite: a new potassium-feldspar polymorph from the Kokchetav ultrahigh-pressure terrane |
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| Authors: | Email author" target="_blank">Shyh-Lung?HwangEmail author Pouyan?Shen Hao-Tsu?Chu Tzen-Fu?Yui Juhn?G?Liou Nikolay?V?Sobolev Ru-Yuan?Zhang Vladislav?S?Shatsky Anton?A?Zayachkovsky |
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| Institution: | (1) Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan, ROC;(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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| 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 +  / -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. |
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