Physical properties:

Chemical formula: Al[SiO4] (F, OH)2
Hardness: 8
SG: 3.53-3.56
Cleavage: Perfect, one direction
Fracture: Fairly brittle
Thermal sensitivity: None

Optical properties:

Refractive index (RI): 1.61-1.638
Dispersion: 0.014 (medium)
Double refraction: 0.008 (weak)
Pleochroism: Variable
Critical angle: 38.5°

Facet angles (pavilion/crown):

Vargas: 42°/41°
Olson: 40°/43°
Soukup: 39°/43°
Roth: 39°/43°
MDR: 39°/43°
Schlagel: 40°/36°
Hashnu: 42°/41°
Sinkankas: 40°/40°
GIA: 39°/43°
Perkins: 39°/43°
Raytech: 40°/39°
Cornwall: 42°/35°
Weikoff: 42°/39°
Carroll: 42.6°/35.3°

Cutting lap:

All grit sizes

Facet polishing:

Vargas: Aluminum oxide on tin or tin/lead
Olson: Aluminum oxide on tin
Soukup: Aluminum or tin oxide on tin or tin/lead
Christiansen: Aluminum oxide on tin or tin/lead (high speed)
Perkins: Diamond on BATT or Corian
MDR: 14-50k diamond on zinc, Aluminum or cerium oxide on acrylic
Raytech: Aluminum oxide on Fast Lap, tin or phenolic

Cabochon polishing:

Christiansen: Aluminum oxide or diamond 50k or 100k on leather or wood


Very important! The basal cleavage plane should not be parallel to any facet. Orient the cleavage at approximately 10° from the table facet or the perpendicular line. Take care of the culet.


Not synthesized. However, synthetic spinel is often sold with the "right" color as topaz. Brown/orange can be heat-treated to white and irradiated to blue. Almost all blue topazes (sky, London, Swiss, electric, neon, etc.) are irradiated and heat-treated.

Topaz rough

Topaz on Gemdat

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