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monocliniccommonSilicates
Biotite
K(Mg,Fe)3AlSi3O10(F,OH)2
Biotite typically forms dark, flaky, platy crystals with a distinct pearly to vitreous luster, often appearing black or dark brown. It is characterized by its perfect basal cleavage, allowing it to be split into thin, flexible sheets.
Biotite Physical Properties
Mohs Hardness
2.5Crystal System
monoclinicLuster
vitreousStreak Color
white to grayish-brownCleavage
perfect basal (one direction)Fracture
unevenSpecific Gravity
2.8Colors
black, dark brown, dark greenTransparency
transparentType Locality
Rössingberge hills, NamibiaMineral Group
SilicatesUses
industrial (insulation, filler), geological indicator, collectorAssociated Minerals
quartz, feldspar, hornblende, muscovite, garnet, tourmalineRarity
commonGeological Context
Biotite is a common rock-forming mineral found in a wide range of igneous rocks (like granite, diorite) and metamorphic rocks (like schist, gneiss). It forms during the cooling and crystallization of magma or through the recrystallization of existing rocks under heat and pressure.
