Almandine
One of six end members of the garnet family. Pure almandine garnets are virtually non-existent. There is always a mixture with pyrope and/or spessartite. To be classed as an almandine SG should be >3.93 and RI >1.77 (There is a small difference in limit values depending on source).
Physical properties:
| Chemistry: | Fe+23Al2(SiO4)3 |
| Hardness: | 7–7,5 |
| SG: | 3,93–4,32 |
| Cleavage: | None |
| Toughness: | Sometimes slightly brittle |
| Heat sensitivity: | None |
Optical properties
| RI: | 1,77–1,83 |
| Dispersion: | 0,024 (medium) |
| Birefringence | None |
| Pleochroism: | None |
| Critical angle: | 34,5° |
Facet angles (pavilion/crown):
| Vargas: | 41°/39° |
| Olson: | 39°/37° |
| Soukup: | 42°/37° |
| Roth: | 42°/37° |
| MDR: | 42°/37° |
| Schlagel: | 40°/36° |
| Hashnu: | 41°/39° |
| Sinkankas: | 40°/40° |
| GIA: | 42°/37° |
| Perkins: | 42°/37° |
| Raytech: | 40°/38° |
| Cornwall: | 41°/34° |
| Weikoff: | 42°/39° |
| Carroll: | 42°/35.3° |
Cutting lap:
Medium – fine
Facet polishing:
| Vargas: | Alumina oxide on tin/lead, tin oxide on tin |
| Olson: | Chrome oxide on tin |
| Soukup: | Alumina oxide on tin or tin/lead |
| Christiansen: | Alumina oxide on tin/lead, tin oxide on tin |
| Perkins: | Alumina oxide on BATT or Corian |
| MDR: | Tin- or alumina oxide on tin, alumina oxide on type metal |
Cabochon polishing:
| Olson: | Chrome oxide on leather |
| Christiansen: | Alumina, tin or chrome oxide on leather or wood |
| Cox: | Alumina or chrome oxide on leather, Cerium oxide on felt |
| Covington: | Chrome or cerium oxide on felt |
Orientation:
For best yield
Treatments/synthetics:
None known
Hint !
Almandine can sometimes be too brittle for new cutting laps.
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