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)Si3O10(OH)2. Crystal structure: monoclinic
Derived forms
biotitic (ˌbaɪəˈtɪtɪk)
adjective
biotite in American English
(ˈbaɪəˌtaɪt)
noun
a dark-colored, soft, monoclinic mica, K(Mg,Fe)3(Al,Fe)Si3O10(OH)2, found in igneous, metamorphic, and sedimentary rocks
Word origin
Ger biotit: so named after J. B. Biot (1774-1862), Fr physicist + -it, -ite1