Peridot

Peridot
General
CategorySilicate minerals
Formula
(repeating unit)
(Mg,Fe)2SiO4
Crystal systemOrthorhombic
Identification
ColorYellow, to yellow-green, olive-green, to brownish, sometimes a lime green, to emerald hue
TwinningUncommon, simple twinning can occur on {100}, {011},{012}, cyclic twinning on {031}
CleavagePoor on {010} and {110}, {010} cleavage improves with increasing iron content
FractureConchoidal
Mohs scale hardness6.5–7
LusterVitreous to oily
StreakColorless
DiaphaneityTranslucent to transparent
Specific gravity3.2–4.3
Refractive index1.64–1.70
Birefringence+0.036
PleochroismWeak pale yellow-green to yellow, yellow to yellow orange
Melting pointbetween 1,200 and 1,900°C
FusibilityInfusible avoid thermal shock
SolubilitySlowly forms gelatinous silica in H Cl

Peridot (/ˈpɛrɪˌdɒt, -ˌd/ 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. Along with diamonds, 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]

  1. ^ "Peridot crystals: Formation & locations". Rock & Gem Magazine. 10 July 2023. Retrieved 21 January 2024 – via rockngem.com. Get to know this August birthstone
  2. ^ "Peridot". Gem notes. geo.utexas.edu. Geology Department. Austin, TX: The University of Texas. course 347k. Retrieved 2024-01-21.
  3. ^ "Color, meanings, and symbolism [of] August birthstone peridot". Old Farmer's Almanac – via almanac.com.