Andalusite
Physical properties:
Chemistry: | Al2SiO5 |
Hardness: | 7–7½ |
SG: | 3.12–3.18 |
Cleavage: | Imperfect, one direction |
Fracture: | Brittle |
Thermal sensitivity: | Low |
Optical properties:
RI: | 1.63–1.64 |
Dispersion: | 0.016 (medium) |
Double refraction: | 0.007 (medium) |
Pleochroism: | Strong |
Critical angle: | 37.5° |
Facet angles (pavilion/crown):
Vargas: | 42°/41° |
Olson: | 40°/43° |
Soukup: | 39°/43° |
Roth: | 39°/43° |
MDR: | 39°/43° |
Schlagel: | 39°/35° |
Hashnu: | 42°/41° |
Sinkankas: | 40°/40° |
GIA: | 39°/43° |
Perkins: | 39°/43° |
Cornwall: | 42°/35° |
Weikoff: | 43°/39° |
Carroll: | 42.6°/35.3° |
Cutting lap:
Medium or fine
Faceting:
Vargas: | Aluminum oxide on tin/lead, tin oxide on tin |
Olson: | Aluminum oxide on tin |
Soukup: | Aluminum oxide on tin |
Christiansen: | Aluminum oxide on tin/lead, tin oxide on tin |
Perkins: | Aluminum oxide on BATT or Corian |
MDR: | Tin oxide on tin |
Cabochon polishing:
Christiansen: | Aluminum oxide on leather, tin oxide on tin |
Orientation:
Based on best color
Treatments/synthetics:
None known
Tips!
The strong pleochroism, brittleness, and cleavage can sometimes be challenging to work with. Avoid sharp corners. Rounded cutting shapes will show the pleochroism clearly.
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