biotite

[ bahy-uh-tahyt ]

Phonetic (Standard)IPA

noun

a very common mineral of the mica group, occurring in black, dark-brown, or dark-green sheets and flakes: an important constituent of igneous and metamorphic rocks.

biotite

/ ˈbaɪəˌtaɪt; ˌbaɪəˈtɪtɪk /

a black or dark green mineral of the mica group, found in igneous and metamorphic rocks. Composition: hydrous magnesium iron potassium aluminium silicate. Formula: K(Mg,Fe) 3 (Al,Fe)Si 3 O 10 (OH) 2 . Crystal structure: monoclinic

biotite

/ bī′ə-tīt′ /

A dark-brown or dark-green to black mica. Biotite is monoclinic and is found in igneous, metamorphic, and sedimentary rocks. Chemical formula: K(Mg,Fe) 3 (Al,Fe)Si 3 O 10 (OH) 2 .

Origin of biotite¹

1860–65; named after J. B. Biot (1774–1862), French mineralogist and mathematician; -ite ¹

Hornblende and biotite are the ferromagnesian constituents and vary much in relative importance.

Biotite, if present, is brown; epidote is yellow or colourless; rutile, apatite and quartz all occur with some frequency.

Minettes contain biotite and orthoclase; kersantites, biotite and plagioclase.

Both in the hand specimens and in microscopic slides of lamprophyric rocks biotite and hornblende are usually conspicuous.

A special group of monchiquites rich in deep brown biotite has been called fourchites (after the Fourche Mountains, Arkansas).

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