Tanzanite and Other Gem-Quality Zoisite

Tanzanite step cut

Color: Blue, violet, purple, orange, brown, colorless and pink, also some collector colors
Moh’s Hardness: 6-6.5
Refractive Index: 1.691-1.70
Critical Angle: 36.28°
Specific Gravity: 3.10-3.37
Cleavage: Perfect in 1 direction
Fracture: Uneven, brittle
Dispersion: .030
Heat Sensitivity: Moderate
Pleochroism: Trichroic – strong. Blue to purple to orange or brown
Birefringence (double refraction): Weak (.006-.009)
Crystal Structure: Orthorhombic

Treatments: Usually heat-treated to change color from orange/brown to blue/purple

What I prefer to polishing with: Alumina oxide on a Tin lap, Spectra Ultralap, 8,000 diamond, 50,000 diamond polish on a Zinc laps

Jeff’s Comments: If cutting before heating orientate the best coffee color up through the table (it will be the best color when heated). Tanzanite can be very brittle and chips easily along keels. I prefer to cut only preheated material because there is some material that will not change to blue/purple. Rough is difficult to find clean.

Design Notes: About any Quartz, Tourmaline or Peridot (and of course Tanzanite) design will work well. As the rough gets more saturated I prefer checker board designs. For light rough I like deep brilliant designs.

Design Links: Cornered -This will work nicely in darker rough