- 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.
Origin of biotite
1860–65; named after J. B. Biot (1774–1862), French mineralogist and mathematician; see -ite1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Examples from the Web for biotite
The minerals at contact are quartz, biotite, magnetite and hornblende.
There is some sericite present, also magnetite, resulting from the decomposition of the biotite.
Biotite occurs in some of these rocks, and melanite also is present.
In other minerals the measurements are not quite the same as in biotite.The Birth-Time of the World and Other Scientific Essays
J. (John) Joly
Biotite and all ferromagnesian minerals rarely appear in them, and never are in considerable amount.
- 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
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
- 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)Si3O10(OH)2.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.