Spinel
Physical properties:
| Chemistry: | MgAl2 O4 |
| Hardness: | 8 |
| SG: | 3.58-3.61 |
| Cleavage: | None |
| Fracture: | Low |
| Thermal sensitivity: | None |
Optical properties:
| RI: | 1.71-1.73 |
| Dispersion: | 0.020 (medium) |
| Double refraction: | None |
| Pleochroism: | None |
| Critical angle: | 35.5° |
Facet angles (pavilion/crown):
| Vargas: | 42°/40° |
| Soukup: | 42°/37° |
| Roth: | 42°/37° |
| MDR: | 42°/37° |
| Schlagel: | 39°/35° |
| GIA: | 42°/37° |
| Perkins: | 42°/37° |
| Raytech: | 40°/38° |
Cutting lap:
All grit sizes
Facet polishing:
| Vargas: | Aluminum oxide on tin/lead or type metal |
| Soukup: | Aluminum oxide on tin |
| Christiansen: | Aluminum oxide on tin or tin/lead, 50-100k diamond on metal disc |
| Perkins: | Diamond on BATT or Corian |
| MDR: | Aluminum oxide on tin, 14 diamond on zinc |
| Raytech: | Aluminum oxide on Fast Lap, tin or phenolic |
Cabochon polishing:
| Christiansen: | 50-100k diamond on leather or wood |
Orientation:
According to shape
Treatments/synthetics:
Synthesized in blue and green colors. Often used to imitate other gemstones.
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