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Olivine is a mineral named for its olive green color. It is a magnesium iron silicate that is one of the most common minerals on the planet. It has several forms with its most famous form being the gem quality mineral peridot which is simply the French name for olivine. Other forms of olivine are produced by differing ratios of iron to magnesium. This produces minerals such as fayolite, forsterite, and chyrsolite. The color can change to a reddish hue if the iron in the composition of the crystal oxidizes. It has a orthorhombic crystalline structure that classifies it as a neosilicate. The structure is based largely around oxygen atoms with the iron, magnesium, and silicon rounding out its composition.
So how is olivine formed? Olivine is very common in the outer mantle of the Earth making up to 50 percent of its composition. Because of it olivine is often found in mafic and ultramafic igneous rocks and in some kinds of metamorphic rock. Magnesium rich olivine is formed by crystallizing from magma that has a high magnesium and a low amount of silica. The magma cools down crystallizing into gabbro and basalt. Magnesium rich olivine can withstand pressures up to 410 kilometers in the Earth and remain stable.
An interesting fact about Olivine is the role the that it plays in plate tectonics. Plate tectonics involves the moving of sections of the Earth’s crust over the mantle. The main process that allows this to happen is solid flow. However solid flow of the Earth’s tectonic plates is possible largely due to the abundance of Olivine in the mantle. It is believed that at high pressures it can hold as much 8900 part million of water which makes olivine more susceptible to solid flow. It is speculated that due to the abundance of olivine in the mantle that the amount of water may be greater than the volume of water found in all the oceans combined.
Olivine is also being considered as a means of helping to control the rampant production of carbon emission. Olive reacts readily in the presence of CO2 and by some measurements less than a liter of olivine mineral could trap all the carbon dioxide produced by burning a liter of fuel. This hold a lot of promise especially since the mineral’s relatively weak structure makes it vulnerable to fast weathering.
We have written many articles about olivine for Universe Today. Here’s an article about chrysolite, and here’s an article about minerals.