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greisen

[grahy-zuh n] /ˈgraɪ zən/
noun
1.
a hydrothermally altered rock of granitic texture composed chiefly of quartz and mica, common in the tin mines of Europe.
Origin
1875-1880
1875-80; < German
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for greisen

greisen

/ˈɡraɪzən/
noun
1.
a light-coloured metamorphic rock consisting mainly of quartz, white mica, and topaz formed by the pneumatolysis of granite
Word Origin
C19: from German, from greissen to split
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Encyclopedia Article for greisen

modification of granite, an intrusive igneous rock; it consists essentially of quartz and white mica (muscovite) and is characterized by the absence of feldspar and biotite. The rock usually has a silvery, glittering appearance from the abundance of layered muscovite crystals, but many greisens resemble a pale granite. The white mica mostly forms large plates with imperfect crystalline outlines. The quartz is rich in fluid enclosures. The most common accessory minerals are tourmaline, topaz, apatite, fluorite, and iron oxides; altered feldspar and brown mica also may be present.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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