Iolite
Also known as cordierite or water sapphire
Physical properties:
| Chemistry: | Mg2Al3[AlSi5O18] |
| Hardness: | 7–7½ |
| SG: | 2.58–2.66 |
| Cleavage: | Imperfect, three directions |
| Fracture: | Somewhat brittle |
| Heat sensitivity: | Low |
Optical properties:
| RI: | 1.53–1.55 |
| Dispersion: | 0.017 (medium) |
| Double refraction: | 0.012 (weak) |
| Pleochroism: | Very strong |
| Critical angle: | 40° |
Facet angles (pavilion/crown):
| Vargas: | 43°/42° |
| Soukup: | 43°/42° |
| Roth: | 43°/42° |
| MDR: | 43°/42° |
| Schlagel: | 42°/38° |
| Sinkankas: | 43°/40-50° |
| GIA: | 43°/42° |
| Perkins: | 42°/38° |
| Cornwall: | 42°/38° |
| Weikoff: | 43°/39° |
| Carroll: | 43°/35.3° |
Cutting lap:
Any grit size
Facet polishing:
| Vargas: | Cerium oxide on acrylic, Aluminum oxide on tin/lead |
| Christiansen: | Aluminum oxide on tin/lead, Tin oxide on tin |
| Perkins: | Aluminum oxide on BATT or Corian |
Cabochon polishing:
| Christiansen: | Aluminum oxide or diamond 50k, 100k on leather or wood, Tin oxide on wood |
Orientation:
Orient carefully to achieve fine blue/violet color. Cleavage planes rarely pose any problems.
Treatments/synthetics:
None known
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