Biotite
Physical Properties
| Color | black |
| Form/Habit | foliated |
| Lusture | vitreous |
| Streak | white |
| Hardness | 2.5-3 |
| Cleavage | perfect 1 set basal |
| Fracture | flaky |
| Specific Gravity | 3 (moderate) |
| Chemical Composition | KAl2(AlSi3O10)(OH)2 |
| Crystal System | monoclinic |
| Diagnostic Properties | foliated form, hardness, perfect 1 set basal cleavage, flaky fractures |