Olivine

Identification and Occurrence

• Olivine is named for its typically olive-green color, thought to be a result of traces of nickel.
• Translucent olivine is sometimes used as a gemstone called peridot.
• Olivine occurs in both mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks.
• Mg-rich olivine crystallizes from magma that is rich in magnesium and low in silica.
• Ultramafic rocks usually contain substantial olivine, and those with an olivine content of over 40% are described as peridotites.
• Mg-rich olivine has been discovered in meteorites, on the Moon, and Mars.
• Olivine has been found falling into infant stars and on asteroid 25143 Itokawa.
• Spectral signatures of olivine have been seen in the dust disks around young stars.
• Olivine has been detected in the tails of comets and in samples from a comet collected by the Stardust spacecraft.
• Magnesium-rich olivine has been detected in the planetesimal belt around the star Beta Pictoris.

Crystal Structure

• Minerals in the olivine group crystallize in the orthorhombic system.
• The structure can be described as a hexagonal, close-packed array of oxygen ions.
• There are three distinct oxygen sites, two distinct metal sites, and only one distinct silicon site.
• The crystal structure of olivine is characterized by isolated silicate tetrahedra.
• Olivine has a Pbnm space group and exists in mirror planes and an inversion center.

High-pressure Polymorphs

• At high temperatures and pressures, olivine undergoes phase transformations.
• The high-pressure polymorphs of olivine include wadsleyite and ringwoodite.
• These high-pressure polymorphs have different crystal structures and properties compared to olivine.
• The presence of water can affect the stability and phase transformations of olivine.
• Understanding the behavior of olivine under high pressures is important for studying Earth's mantle and geodynamic processes.

Industrial and Historical Uses

• Olivine has industrial applications in metalworking processes.
• It has been used as a refractory material in high-temperature applications.
• Olivine has historical uses as a gemstone, particularly as peridot or chrysolite.
• The finest gem-quality olivine has been obtained from Zabargad Island in the Red Sea.
• Olivine's unique properties and abundance make it a versatile and valuable mineral in various industries.

Olivine Weathering and Uses

• Olivine undergoes phase transitions at certain depths within the Earth's mantle.
• These phase transitions affect the density of the mantle and mantle convection.
• The pressure at which these phase transitions occur depends on temperature and iron content.
• Olivine is unstable on the Earth's surface and easily alters into iddingsite in the presence of water.
• The presence of iddingsite on Mars suggests the existence of liquid water in the past.
• Olivine can be used to sequester carbon dioxide (CO2) through enhanced weathering.
• Crushed olivine weathers completely within a few years, sequestering CO2 from the atmosphere.
• Olivine is used as a substitute for dolomite in steel works.
• The aluminium foundry industry uses olivine sand for casting objects in aluminium.
• Olivine is marketed as an ideal rock for sauna stoves in Finland due to its high density and resistance to weathering.

Olivine Data Sources