Peridot
Peridot (/ˈpɛrɪˌdɒt, -ˌdoʊ/ PERR-ih-dot, -doh), sometimes called chrysolite, is a yellowish-green transparent variety of olivine. Peridot is one of the few gemstones that occur in only one color.
| Peridot | |
|---|---|
| General | |
| Category | Silicate minerals |
| Formula (repeating unit) | (Mg, Fe)2SiO4 |
| Crystal system | Orthorhombic |
| Identification | |
| Color | Yellow, to yellow-green, olive-green, to brownish, sometimes a lime green, to emerald-ish hue |
| Twinning | Uncommon, simple twinning can occur on {100}, {011},{012}, cyclic twinning on {031} |
| Cleavage | Poor on {010} and {110}, {010} cleavage improves with increasing iron content |
| Fracture | Conchoidal |
| Mohs scale hardness | 6.5–7 |
| Luster | Vitreous to oily |
| Streak | Colorless |
| Diaphaneity | Translucent to transparent |
| Specific gravity | 3.2–4.3 |
| Refractive index | 1.64–1.70 |
| Birefringence | +0.036 |
| Pleochroism | Weak pale yellow-green to yellow, yellow to yellow orange |
| Melting point | Very high |
| Fusibility | Infusible avoid thermal shock |
| Solubility | Slow in HCl to form gelatinous silica |
Peridot can be found in mafic and ultramafic rocks occurring in lava and peridotite xenoliths of the mantle. The gem occurs in silica-deficient rocks such as volcanic basalt and pallasitic meteorites. Peridot is one of only two gems observed to be formed not in Earth's crust, but in the molten rock of the upper mantle. Gem-quality peridot is rare on Earth's surface due to its susceptibility to weathering during its movement from deep within the mantle to the surface. Peridot has a chemical formula of (Mg, Fe)2SiO4. Peridot is one of the birthstones for the month of August.