Biotite
Chemical Formula	K(Mg,Fe)3(AlSi3O10)(F,OH)2
Species	Silicates
Crystal System	Monoclinic
Mohs Scale	2.5-3
Specific Gravity	2.7-3.1
Color	Dark brown, greenish brown, blackish brown, yellow, white
Streak	White
Luster	Vitreous to pearly
Refractive Index	nα = 1.565–1.625nβ = 1.605–1.675nγ = 1.605–1.675
Diaphaneity	transparent to translucent to opaque
Cleavage	Perfect on the
Fracture	Micaceous
Crystal Habit：massive to platy