Zircon
The yellow-orange variety was historically called "hyacinth," and it is a gemstone widely found as an accessory mineral in rocks such as granite. Because it contains U and Th, if its crystal structure is damaged by radiation, it undergoes metamictization, resulting in a decrease in hardness and specific gravity. It is characterized by high dispersion, a brilliant luster, and doubling due to birefringence.
Available in a variety of colors, such as blue, colorless, and golden yellow (many derived from heat treatment)
Basic Information
| English Name | Zircon |
|---|---|
| Japanese Name | Hyacinth stone |
| Chemical Composition | Zr(SiO4) |
| Crystal System | Tetragonal |
| Hardness | 6.5–7.5 (depends on the degree of crystal damage) |
| Specific Gravity | Approx. 4.0 (High-type is 4.67–4.70) |
Types, Colors, Treatments, and Similar Stones
- Structural Type: High / Medium / Low (depending on progress of metamictization).
- Color: Changes from colorless to brown to green with increasing damage. Most blue, white, and colorless stones are heat-treated (blue is traded under the name "Starlite").
- Varieties: Zircon cat's eye, parti-colored (yellow-green / yellow-brown, etc.).
- Treatment Precautions: Can become brittle with heat treatment.
- Similar Stones: Yellow to brown varieties resemble garnet, and green varieties resemble tourmaline. *Cubic Zirconia is a synthetic zirconium oxide (ZrO2) and is a completely different material.