Zircon
Comes in two forms: high or normal zircon with good physical and optical properties, and low zircon (green) where radioactive decay has progressed to the point that they can be almost amorphous in structure and their properties are much lower (SG 4.0, RI 1.80, critical angle 34°).
Physical properties:
Chemistry: | Zr[SiO4] |
Hardness: | 7½ |
SG: | 4.6 – 4.7 |
Cleavage: | Imperfect, two directions |
Fracture: | Brittle |
Heat sensitivity: | None |
Optical properties:
RI: | 1.92–2.01 |
Dispersion: | 0.038 (medium) |
Double refraction: | 0.06 (high) |
Pleochroism: | Weak |
Critical angle: | 31° |
Facet angles (pavilion/crown):
Vargas: | 41°/37° |
Soukup: | 42°/37° |
Roth: | 41°/35° |
MDR: | 41°/35° |
Schlagel: | 40°/36° |
Hashnu: | 41°/37° |
Sinkankas: | 40°/40° |
GIA: | 41°/40° |
Perkins: | 39°/43° |
Raytech: | 42°/37° |
Cornwall: | 38°/32° |
Weikoff: | 42°/35° |
Carroll: | 41.6°/35.3° |
Cutting lap:
All grit sizes
Facet polishing:
Vargas: | Aluminium oxide on tin/lead or tin |
Soukup: | Aluminium oxide on tin |
Christiansen: | Aluminium oxide on tin/lead or tin, diamond 50k/100k on steel |
Perkins: | Aluminium oxide on BATT or Corian |
MDR: | Aluminium oxide on tin, 14-50k diamond on zinc |
Raytech: | Aluminium oxide on Fast Lap, tin or phenolic |
Cabochon polishing:
Christiansen: | Aluminium oxide, tin oxide, or diamond 50k or 100k on leather or wood |
Orientation:
The high double refraction can make larger stones appear "blurry" if the table facet is not perpendicular to the crystal axis.
Treatments/synthetics:
Brown stones are heat-treated to become blue or colorless.
Tips!
Do not confuse it with the synthetic material cubic zirconia, which has completely different properties.
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