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 for best yield.
I think Zircons are actually one of the most over looked stones by hobby cutters, there is a lot of quality Zircon rough available for reasonable prices.
Design Notes: About any design will work well. On light colored stones I prefer a deep design and tend to cut designs with more facets.
Design Links: Gram Prince – Nice rectangle and fairly deep
Gram Princess – My princess design for colored stones
Gram Portuguese – Classic round optimized by me, if you have a stone large enough
White Asterism – Nice for light materials
Simple Portuguese – Less facets for a smaller stone
Rainbow – Classic 1.33 oval