What is Olivine?
Olivine is a major rock-forming silicate group and one of the most recognisable green minerals in igneous and planetary rocks.
Mineralogy and crystal structure
Reference formula: (Mg,Fe)2SiO4. Olivine is a solid-solution series between forsterite and fayalite. The displayed COD model is a representative forsterite-rich structure; iron-magnesium proportions vary between specimens and control density and colour. Olivine is classified with silicates and has a orthorhombic crystal system. Typical hardness is 6.5–7 on the Mohs scale and specific gravity is approximately 3.2–4.4.
Colour, lustre and habit
Typical colours include olive-green, yellow-green, brown, colourless. The usual granular, prismatic, massive habit and vitreous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Olivine forms in or is associated with mantle peridotite, basaltic and ultramafic magmas, metamorphic rocks and some meteorites. Important documented localities include Hawaii, Arizona, Pakistan, Myanmar, Norway, South Africa and meteorite falls worldwide.
The green mineral of the mantle
Olivine connects a polished peridot to the deep Earth. Its orthorhombic silicate framework is stable in the mantle and also survives in lava, meteorites and planetary crusts.
Collecting and care
Protect gem-quality peridot from impact and acids; retain locality and disclose that peridot is the gem variety of olivine.
