K(Fe,Mg)3AlSi3O10(OH)2Monoclinic
Biotite
K(Fe,Mg)3AlSi3O10(OH)2
SilicatesChemical FormulaK(Fe,Mg)3AlSi3O10(OH)2
Crystal SystemMonoclinic
Mohs Hardness2.5
Specific Gravity3.1
ColorBlack to dark brown
LusterVitreous to pearly
StreakWhite to gray
CleavagePerfect basal
FractureFlexible sheets
Occurrence
Dark mica found in igneous and metamorphic rocks. Common in granite.