Turquoise is a porous, semitranslucent to opaque hydrated copper and aluminum phosphate. It forms when copper-rich groundwater reacts with minerals that contain phosphorus and aluminum.
Properties
| Refractive index | 1.610 to 1.650; spot reading usually about 1.61 to 1.62 |
|---|---|
| Birefringence | Not measurable (an aggregate) |
| Optic character | Aggregate |
| Dispersion | Not given by our sources |
| Specific gravity | 2.76 (+0.14, -0.36) |
| Hardness (Mohs) | 5 to 6 |
| Crystal system | Aggregate (triclinic) |
| Pleochroism | Weak: colorless, pale blue, pale green |
| Absorption spectrum | Weak band in the violet, seen with a desk-model spectroscope, 430 nm (Fe3+) |
Published values. They change a little from stone to stone. Our tools do not model turquoise yet. Sources: GIA · International Gem Society
In more detail
Remnants of the host rock can show as splotches or veins, called matrix. Coarse, porous stones are usually treated to make them smoother and shinier. Heat, chemicals, cosmetics and even skin oils can discolor it. Never clean it with steam or ultrasonic cleaners.
Related terms
- Treatment: A treatment is any process, other than cutting and polishing, that changes a gem's color or apparent clarity. Anyone who sells a treated gem must disclose the treatment.
- Resin filling: Resin filling is filling a gem's fissures or cavities with a resin, often one that hardens, to hide them.
- Dyeing: Dyeing is adding a colored substance to a gem's fractures or pores to change its color.
- Cabochon: A cabochon is a gem polished to a smooth, convex dome, with no facets. It is one of the oldest and simplest cuts.
- Stability: Stability is a gem's resistance to damage from heat, light and chemicals.