Peridot

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 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	between 1,200 and 1,900°C
Fusibility	Infusible avoid thermal shock
Solubility	Slowly forms gelatinous silica in H Cl

Peridot (/ˈpɛrɪˌdɒt, -ˌdoʊ/ PERR-ih-dot, -⁠⁠doh), sometimes called chrysolite, is a yellow-green transparent variety of olivine. Peridot is one of the few gemstones that occur in only one color.

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.^[1] Gem-quality peridot is rare on Earth's surface due to its susceptibility to alteration during its movement from deep within the mantle and weathering at the surface.^[2] Peridot has a chemical formula of (Mg,Fe)₂SiO₄.

Peridot is one of the birthstones for the month of August.^[3]