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.

Andalusite rough

Andalusite on Gemdat


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