christmas mineral advent calendar

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Geology Chronicles is running a Christmas Mineral Advent Calendar!

Olivine is named for its typically olive-green color (thought to be a result of traces of nickel), though it may alter to a reddish color from the oxidation of iron.

Translucent olivine is sometimes used as a gemstone called peridot (péridot, the French word for olivine). It is also called chrysolite (or chrysolithe, from the Greek words for gold and stone). Some of the finest gem-quality olivine has been obtained from a body of mantle rocks on Zabargad island in the Red Sea. It is a common mineral in the Earth’s subsurface but weathers quickly on the surface.

The name “Peridot” is believed to have originated from the Arabic word faridat, meaning “gem”, or alternatively, as the Oxford English Dictionary suggests, it came from classical Latin pæderot - a kind of opal

The ratio of magnesium and iron varies between the two endmembers of the solid solution series: forsterite (Mg-endmember) and fayalite (Fe-endmember). Olivine gives its name to the group of minerals with a related structure (the olivine group) which includes tephroite, monticellite and kirschsteinite.

Olivine/peridot 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. That magma crystallizes to mafic rocks such as gabbro and basalt. Ultramafic rocks such as peridotite and dunite can be residues left after extraction of magmas, and typically they are more enriched in olivine after extraction of partial melts. Olivine and high pressure structural variants constitute over 50% of the Earth’s upper mantle, and olivine is one of the Earth’s most common minerals by volume.