Physical properties:

Chemistry: MgAlO4
Hardness: 8
SG: 3.58-3.61
Cleavage: None
Fracture: Low
Thermal sensitivity: None

Optical properties:

RI: 1.71-1.73
Dispersion: 0.020 (medium)
Double refraction: None
Pleochroism: None
Critical angle: 35.5°

Facet angles (pavilion/crown):

Vargas: 42°/40°
Soukup: 42°/37°
Roth: 42°/37°
MDR: 42°/37°
Schlagel: 39°/35°
GIA: 42°/37°
Perkins: 42°/37°
Raytech: 40°/38°
Cornwall: 41°/34°
Weikoff: 42°/39°
Carroll: 42.2°/35.3°

Cutting lap:

All grit sizes

Facet polishing:

Vargas: Aluminum oxide on tin/lead or type metal
Soukup: Aluminum oxide on tin
Christiansen: Aluminum oxide on tin or tin/lead, 50-100k diamond on metal disc
Perkins: Diamond on BATT or Corian
MDR: Aluminum oxide on tin, 14 diamond on zinc
Raytech: Aluminum oxide on Fast Lap, tin or phenolic

Cabochon polishing:

Christiansen: 50-100k diamond on leather or wood


According to shape


Synthesized in blue and green colors. Often used to imitate other gemstones.

Spinell on Gemdat

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