Sillimanite
Physical Properties
| Color | brown |
| Form/Habit | acicular |
| Lusture | vitreous |
| Streak | white |
| Hardness | 7 |
| Cleavage | perfect 1 set rarely seen |
| Fracture | uneven |
| Specific Gravity | 3.23 (moderate) |
| Chemical Composition | Al2SiO5 |
| Crystal System | orthorhombic |
| Diagnostic Properties | acicular habit, hardness, perfect 1 set cleavage |