Chrysoberyl
Gold to green to brown. Alexandrite is a rare variety that changes color from green in daylight to red under incandescent light.
Physical Properties:
| Chemistry: | BeAl2O4 |
| Hardness: | 8½ |
| SG: | 3.70-3.72 |
| Cleavage: | Imperfect in two directions |
| Fracture: | None |
| Thermal sensitivity: | None |
Optical Properties:
| RI: | 1.744-1.755 |
| Dispersion: | 0.015 (medium) |
| Birefringence: | 0.011 (medium) |
| Pleochroism: | Weak (strong in Alexandrite) |
| Critical angle: | 35° |
Faceting angles (pavilion/crown):
| Vargas: | 42°/40° |
| Olson: | 39°/37° |
| Soukup: | 42°/37° |
| Roth: | 42°/37° |
| MDR: | 42°/37° |
| Schlagel: | 40°/36° |
| Hashnu: | 42°/39° |
| Sinkankas: | 40°/40° |
| GIA: | 42°/37° |
| GIA: | 42°/37° |
| Cornwall: | 40°/34° |
| Weikoff: | 42°/38° |
| Carroll: | 42.1°/35.3° |
Cutting lap:
All grit sizes
Faceting:
| Vargas: | Diamond 100k on ceramic (low speed), aluminum oxide on tin/lead |
| Olson: | Diamond 14k on tin |
| Soukup: | Aluminum oxide on tin/lead, copper |
| Christiansen: | Aluminum oxide on tin/lead, diamond 50k, 100k on tin, tin/lead, copper |
| Herbst: | Diamond or aluminum oxide on metal or composite disc |
| Perkins: | Diamond on BATT |
Cabochon polishing:
| Christiansen: | Diamond 50k, 100k on wood or hard leather |
Orienting:
According to shape. Alexandrite must be oriented by color.
Treatments/Synthetic:
Can be irradiated to enhance color. Sometimes alexandrite is oil-treated. Alexandrite is synthesized. A synthetic corundum with a color change from bluish-green to purple is often incorrectly called alexandrite.
Tips!
Polishing with aluminum oxide is slow but gives good results. With diamond on a softer disc (metal), you can increase the speed.
There are no products to list in this category.