biotite (bī`ətīt'), iron-rich variety of phlogopite, most abdunant of the mica mica (mī`kə), general term for a large group of minerals, hydrous silicates of aluminum and potassium, often containing magnesium,
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Silicate mineral in the common mica group. It is abundant in metamorphic rocks, in pegmatites, and in granites and other igneous rocks. Biotite is a layer silicate structure in which aluminum and silicon occur in infinitely extending Si-Al-O sheets that alternate with potassium-rich and magnesium- (and iron-) containing sheets.
biotite [′bīยทə‚tīt]
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biotite
or black mica)
Biotite mica from the district of Juchitán, Oaxaca, Mex.
(credit: Courtesy of the Field Museum of Natural History, Chicago; photograph, John H. Gerard-EB Inc.)
biotite [′bīยทə‚tīt]
(mineralogy)
A black, brown, or dark green, abundant and widely distributed species of rock-forming mineral in the mica group; its chemical composition is variable: K2[Fe(II),Mg]6-4[Fe(III),Al,Ti]0-2(Si6-5,Al2-3)O20-22(OH,F)4-2. Also known as black mica; iron mica; magnesia mica; magnesium-iron mica.
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