Biotite is a phyllosilicate (sheet silicate) mica mineral.
Pronunciation: BUY•oh•tight (accent on capitalized syllable)
Color: black, dark green, dark brown
Streak: --
Luster: splendent (very shiny)
Diaphaneity: translucent; may appear opaque in hand specimen
Hardness: 2.5-3
Specific gravity:2.8-3.2
Cleavage/fracture: 1 -- breaks in paper-thin flexible elastic sheets
Other distinguishing properties: The black color and thin elastic cleavage sheets are diagnostic; found in many types of igneous and metamorphic rocks.
Klein, C., and Hurlbut, C.S., Jr., 1999, Manual of Mineralogy (after James D. Dana) [21st edition, revised]: New York, John Wiley & Sons, 682 p.
Los Angeles County Museum of Natural History, The Photo Atlas of Minerals: nhm.org/pam/
Return to the Minerals page.
