biotite

[bahy-uh-tahyt]

noun

1. 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 /

noun

1. 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

1. 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 .

Other Word Forms

• biotitic adjective

Word History and Origins

Origin of biotite¹

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

Example Sentences

Each mineral may also enclose particles of the others; in the quartz, for example, small crystals of graphite, biotite, iron oxides, sillimanite or felspar may appear in great numbers.

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The snowy white feldspar and quartz set off the glittering crystals of hornblende and biotite wonderfully.

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The biotite is brown; the hornblende brown or greenish brown; the augite usually green.

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The commonest accessory minerals are tourmaline, topaz, apatite, fluorspar and iron oxides; a little felspar more or less altered may also be present and a brown mica which is biotite or lithionite.

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Exceptions to this sequence are unusual; sometimes the first of the felspars have preceded the hornblende or biotite which may envelop them in ophitic manner.

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