Amethyst
Lilac to violet variation of crystalline quartz
Physical properties:
| Chemistry: | SiO2 |
| Hardness: | 7 |
| SG: | 2.65-2.66 |
| Cleavage: | None |
| Fracture: | Conchoidal, moderately brittle |
| Heat sensitivity: | None |
Optical properties:
| RI: | 1.54-1.55 |
| Dispersion: | 0.013 (moderate) |
| Double refraction: | 0.009 (weak) |
| Pleochroism: | Weak to distinct, purple and reddish-lilac |
| Critical angle: | 40° |
Facet angles (pavilion/crown):
| Vargas: | 43°/42° |
| Olson: | 43°/42° |
| Soukup: | 43°/42° |
| Roth: | 43°/42° |
| MDR: | 43°/42° |
| Schlagel: | 42°/38° |
| Hashnu: | 43°/42° |
| Sinkankas: | 43°/40-50° |
| GIA: | 43°/42° |
| Perkins: | 43°/42° |
| Raytech: | 43°/42° |
| Cornwall: | 44°/36° |
| Weikoff: | 43°/42° |
| Carroll: | 43°/35.3° |
Cutting lap:
All grit sizes
Facet polishing:
| Vargas: | Cerium oxide on acrylic, Aluminum oxide on tin or tin/lead |
| Olson: | Tin or cerium oxide on acrylic or tin, Ultralap |
| Christiansen: | Cerium oxide on acrylic, Aluminum oxide on tin or tin/lead |
| Raytech: | Aluminum or tin oxide on Fast Lap, tin or phenolic |
| MDR: | Tin or cerium oxide on acrylic or tin |
Cabochon polishing:
| Olson: | Tin or cerium oxide on felt |
| Christiansen: | Aluminum, tin, or cerium oxide on felt/leather |
| Cox: | Cerium oxide on felt/leather |
| Covington: | Cerium oxide on felt/leather |
Orientation:
According to color banding and with color centers in the culet.
Treatments/synthetics:
There is plenty of synthetic amethyst available on the market.
Tips!
Sometimes difficult to polish on plexiglass (acrylic, lucite); try using aluminum oxide on tin lap or LightningLap A1.
LightningLap with cerium oxide is excellent for polishing large facets.
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