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plagioclase |
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plagioclaseAny member of the series of abundant feldspar minerals that usually occur as light- to medium-grey-coloured, transparent to translucent grains or crystals. Plagioclase ranges in composition from albite to anorthite. It is used in the manufacture of glass and ceramics; iridescent varieties are valued as gemstones. The primary importance of plagioclase, however, derives from its role as a rock-forming mineral. plagioclase [′plā·jē·ə‚klās] (mineralogy) A type of triclinic feldspars having the general formula (Na,Ca)Al(Si,Al)Si2O8; they are common rock-forming minerals. A series in the plagioclase group which can be divided into a number of varieties based on the relative proportion of the solid solution end members, albite and anorthite (An): albite (An 0-10) oligoclase (An 10-30), andesine (An 30-50), labradorite (An 50-70), bytownite (An 70-90), and anorthite (An 90-100). Also known as sodium-calcium feldspar. How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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| Despite the inclusion of statements such as 'all contain sanidine in the groundmass as well as significant amounts of plagioclase . The mineralogy is 40% plagioclase (3% of which is myrmekitic), 29% quartz, 28% potassium feldspar (microcline and orthoclase), 3% biotite, with trace magnetite and rare epidote and chlorite. About half of MSH is crystalline in nature, primarily plagioclase, a series of compounds beginning with sodium aluminum silicate (NaAl[Si. |
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