Prehnite
From The Gemology Project
| Prehnite | ||
|---|---|---|
| Chemical composition | Ca2Al2Si3O10(OH)2+Fe | |
| Crystal system | Orthorhombic | |
| Habit | Usually Fibrous Aggregate | |
| Cleavage | Good:1 direction | |
| Fracture | Uneven-Conchoidal | |
| Hardness | 6-6.5 | |
| Optic nature | Biaxial (+) Aggregate | |
| Refractive index | 1.649-1.616 | |
| Birefringence | .020-0.031 | |
| Specific gravity | 2.90 | |
| Lustre | Vitreous-Pearly | |
