Biotite

K(Mg,Fe++)3[AlSi3O10(OH,F)2

Cleavage: [001] Perfect
Color: Dark brown, Greenish brown, Blackish brown, Yellow, White. Density: 2.8 - 3.4, Average = 3.09
Diaphaniety: Transparent to translucent to opaque
Fracture: Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern.
Habits: Micaceous - Platy texture with "flexible" plates., Lamellar - Thin laminae producing a lamellar structure., Pseudo Hexagonal - Crystals show a hexagonal outline.
Hardness: 2.5-3 - Finger Nail-Calcite
Luminescence: None.
Luster: Vitreous - Pearly
Streak: gray