Color: Colorless, yellow, brown, red, blue, green, orange, violet and pink, about any color. I classify fancy Zircons as unusual or different than the norm. Unusual color.
Moh’s hardness: 6.5-7.5
Type – Normal (high RI): Sometimes called high Zircon 1.94-1.987 normal (higher refractive index) zircon is usually found in crystal form.
Critical Angle: 30.33°
Type – Metamict (lower RI): sometimes called low Zircon: 1.777-1.79 Metamict (lower refractive index) Zircon is usually found as river-worn pebbles
Critical Angle: 34.40°
Specific Gravity: 3.9-4.71
Cleavage: Imperfect 2 directions.
Fracture: Conchoidal, very brittle.
Heat Sensitivity: Yes, in my experience
Dichroic: Moderate to weak depending on color
Birefringence (double refraction): Strong (.06)
Crystal structure: Tetragonal
Treatments: Generally none, can be heated.
What I prefer to polishing with: Alumina oxide with a tin lap (scored). Diamond on tin laps works too.
Jeff’s Comments: Cuts and polishes with not much trouble. Be careful when heating for dopping. If there as any cleavage (for example on the edge of the rough) heating can cause it to run. Grind off any thing that you see like this before dopping. Orientating for the “c” axis is preferred (to minimize the double refraction), but I generally cut