Olivine forms a continuous solid-solution series between magnesium-rich forsterite (Mg₂SiO₄, melting near 1,900 °C) and iron-rich fayalite (Fe₂SiO₄, melting near 1,200 °C), with transparent gem-quality crystals known as peridot.
Constituting more than 50% of Earth's upper mantle down to ~410 km depth, olivine transforms under higher mantle pressures into wadsleyite (410–520 km), spinel-structured ringwoodite (520–660 km), and finally bridgmanite plus ferropericlase.
Among the first minerals to crystallize from mafic magma in Bowen's reaction series, olivine weathers rapidly at Earth's surface via hydrolysis into iddingsite and magnesium carbonates, making crushed olivine a candidate for coastal CO₂ sequestration.