Olivine : mineral present in igneous rocks (basalt, gabbro, peridotite) associated with plagioclase and pyroxene. This mineral is generally present in the form of aggregates, with more or less rounded grains.
Olivine is a binary system with compositions of the two poles forsterite and fayalite. Thus, depending on their origin, the proportions of Mg2+ and Fe2+ vary. Forsterite (Mg2SiO4) is the term containing no iron, while fayalite (Fe2SiO4) contains no magnesium.
Cottages and deposits of olivine
Olivine is a mineral that occurs in the Earth's crust and makes up over 50% of the Earth's mantle. It is the most abundant and common mineral on Earth. Olivine is found in igneous rocks (rocks of volcanic origin), but can also be found in metamorphic rocks. Indeed, olivine can occur during the transformation of pre-existing rocks at high pressures and temperatures.
Example of volcanic rocks containing olivine:
- Peridotite, a mantle rock with 90% olivine dunite.
Example of metamorphic rocks containing olivine:
- Dolomitic limestone
The occurrence of olivine-bearing rocks is abundant in the world as shown on this map from the Vesta Project.
Despite the abundance of olivine on Earth, not all countries exploit rocks containing olivine.
In France, the deposits present are not equivalent to those of the producing countries. According to BRGM, there are sites of peridotite deposits, notably in Corsica, the Pyrenees, the Massif Central, the Alps, the Vosges and Brittany. However, the percentage of olivine is too low to consider its exploitation. As it does not have sufficient commercial value, France imports olivine.
According to the Mineral Industry, in 2010, the main producing countries of olivine are: Norway, Sweden, Italy, Turkey, Spain and the USA. Norway has the world's largest deposit and mines dunite rocks.
Exploration of olivine rock deposits is easy because the rock outcrops as a ridge or dome. In general, dunite rocks, which contain 90% olivine, are mined in open pits, with the exception of an underground mine in Norway. According to BRGM, 80% of the olivine consumed in the world is used by industry for the production and transformation of metals. For example, in France, olivine is used in the steel industry, in foundry sand, in the manufacture of refractories, in pressure water jet cutting and as a sandblasting abrasive.
Today, olivine can be used for purposes other than the industrial world, in particular, with the dissipation of fine grains on land and beaches for the sequestration of CO2 and thus, the reduction of greenhouse gas emissions. This process is based on the enhanced weathering of rocks through the carbon mineralisation process, mineral carbonation.