biotitePronunciation: /ˈbʌɪətʌɪt/Definition of biotite noun [mass noun] a black, dark brown, or greenish black micaceous mineral, occurring as a constituent of many igneous and metamorphic rocks. Origin: mid 19th century: named after J.-B. Biot (1774–1862), French mineralogistbiotite in other Oxford dictionaries Definition of biotite in the US English dictionary