Olivine facts for kids

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Olivine
Olivine-gem7-10a.jpg
General
Category Nesosilicate
Olivine group
Olivine series
Formula
(repeating unit)
(Mg, Fe)2SiO4
Strunz classification 9.AC.05
Identification
Color Yellow to yellow-green
Crystal habit Massive to granular
Crystal system Orthorhombic
Cleavage Poor
Fracture Conchoidal – brittle
Mohs scale hardness 6.5–7
Luster Vitreous
Streak None
Diaphaneity Transparent to translucent
Specific gravity 3.2–4.5
Optical properties Biaxial (+)
Refractive index nα = 1.630–1.650
nβ = 1.650–1.670
nγ = 1.670–1.690
Birefringence δ = 0.040
Olivine (peridot)
Olivine (Peridot)

Olivine (or chrysolite) is a mineral made of magnesium iron silicate with the formula (Mg,Fe)2SiO4

It ranges in colour from chartreuse green to pale olive. In its gem form, it is called peridot.

Dunite is a rock of 90%+ olivine. Dunite and other peridotite rocks are major constituents of the Earth's mantle above a depth of about 400 kilometers. Dunite is rarely found on land, except where slabs of mantle rock from a subduction zone have been thrust onto continental crust. Olivine has also been found at several extraterrestrial locations, such as the moon and many passing space rocks - as well as the outer layers of dust orbiting young stars.

Uses

Olivine is used as a substitute for dolomite in steel works. Olivine is also used to tap blast furnaces in the steel industry, acting as a plug, removed in each steel run.

The aluminium foundry industry uses olivine sand to cast objects in aluminium. Olivine sand requires less water than silica sands while still holding the mold together during handling and pouring of the metal. Less water means less gas (steam) to vent from the mold as metal is poured into the mold.

In Finland, olivine is marketed as an ideal rock for sauna stoves because of its comparatively high density and resistance to weathering under repeated heating and cooling.

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