Olivine

Lore & Background

Olivine is named for its typically olive-green color, thought to result from traces of nickel, though it may alter to reddish from iron oxidation. Translucent olivine is used as the gemstone peridot, also called chrysolite. Some of the finest gem-quality olivine has come from mantle rocks on Zabargad Island in the Red Sea. The mineral occurs in mafic and ultramafic igneous rocks and certain metamorphic rocks. Mg-rich olivine crystallizes from magma low in silica, forming rocks such as gabbro, basalt, peridotite, and dunite. Fe-rich fayalite is rarer, found in some granites and rhyolites, and can coexist with quartz.

Reader's Guide

Olivine's significance lies in its dominance of Earth's upper mantle, where it constitutes over 50% of the volume and influences the solid flow that drives plate tectonics. Experiments show that at high pressures, olivine can dissolve substantial water, potentially holding more water than Earth's oceans, and that water content drastically reduces its resistance to flow. Its phase transitions at depth—to wadsleyite, ringwoodite, and then perovskite—create seismic discontinuities and affect mantle convection. Olivine weathers rapidly on the surface, altering to iddingsite, and its presence on Mars suggests past liquid water. Artificially increasing olivine weathering has been proposed for CO2 sequestration. Norway produces about 50% of the world's industrial olivine. Extraterrestrially, Mg-rich olivine has been found in meteorites, on the Moon, Mars, asteroid Itokawa, and in comet dust.

Did You Know?

• Olivine is named for its typically olive-green color, thought to result from traces of nickel.
• Olivine and its high-pressure variants constitute over 50% of Earth's upper mantle.
• The spectral signature of olivine has been detected in comet tails and dust disks around young stars.