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

/ bī′ə-tīt′ /

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 .

Derived Forms

• biotitic, adjective

Other Words From

• bi·o·tit·ic [bahy-, uh, -, tit, -ik], 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

Slates, shales and clays yield biotite hornfelses in which the most conspicuous mineral is black mica, in small scales which under the microscope are transparent and have a dark reddish-brown colour and strong dichroism.

From Project Gutenberg

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

From Scientific American

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

From Project Gutenberg

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.

From Project Gutenberg

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.

From Project Gutenberg