Petalite
Physical properties:
| Chemistry: | (Li,Na) [AlSi4O10] |
| Hardness: | 6-6½ |
| SG: | 2.40 |
| Cleavage: | Perfect, one direction |
| Fracture: | Brittle |
| Heat sensitivity: | Low |
Optical properties:
| RI: | 1.502–1.518 |
| Dispersion: | >0.014 (medium) |
| Birefringence: | >0.012 (medium) |
| Pleochroism: | None |
| Critical angle: | 41.7° |
Facet angles (pavilion/crown):
| Vargas: | >43°/42° |
| Sinkankas: | 43°/40-50° |
| GIA: | 43°/42° |
Cutting lap:
Medium to fine
Facet polishing:
| Vargas: | Cerium oxide on acrylic, Aluminium oxide on tin/lead (low speed) |
| Christiansen: | Cerium oxide on acrylic, Aluminium oxide on tin/lead (low speed) |
Cabochon polishing:
| Christiansen: | Aluminium oxide on leather, Cerium oxide on felt |
Orienting:
Ensure that the table facet is not parallel to the cleavage.
Treatments/synthetics:
None known
Tips!
With careful handling (no coarse cutting laps!), Petalite rarely presents any problems.
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