Biotite is a common ferromagnesian mica occurring in igneous and metamorphic rocks. Its iron–magnesium composition varies with pressure–temperature conditions, making it an important index mineral for assessing metamorphic grade and in deciphering tectono-thermal evolution of the continental crust. #GeologicalSurveyofIndia #MineraloftheWeek #Biotite #Mica #GeoPedia #Geologykefunde | Geological Survey of India

Biotite Granite Biotite granite is a coarse-grained intrusive igneous rock composed mainly of quartz, feldspar (both plagioclase and K-feldspar), and biotite mica as the dominant dark mineral. It typically forms deep within the continental crust as a result of slow cooling and solidification of silica-rich magma. Key Characteristics • Texture: Phaneritic (coarse-grained); crystals visible to the naked eye • Color: Generally light-colored (grey to pink), speckled with black biotite flakes • Major