Olivine (mineral)
Olivine is a high-temperature mineral group that predominantly consists of two end members: forsterite (rich in magnesium) and fayalite (rich in iron). This mineral typically exhibits a range of colors, including yellowish-green, yellowish-brown, and sometimes even reddish hues. Olivine is a significant component of the Earth's lower crust and upper mantle, often found in volcanic rocks, particularly basalt. It is also one of the primary minerals found in certain types of meteorites. The main practical application of olivine is the gemstone known as peridot, which is valued for its clarity and vibrant colors, particularly the dark yellow-green variety. Notable sources of high-quality peridot include the San Carlos Indian Reservation in Arizona and the Red Sea island of Zebirget. Olivine crystals are typically transported to the surface through explosive volcanic activity, where they can be found scattered in lava flows or as part of xenoliths, which are rocks formed at greater depths. Peridot, which is the birthstone for August, is the most recognized form of olivine used in jewelry.
Olivine (mineral)
Where Found
Olivine is common in the Earth’s crust. Large deposits of olivine are often associated with certain volcanoes.
Primary Uses
The main use of olivine is the use of peridot as a gemstone, which is found in Arizona and on the Red Sea island of Zebirget. Through chemical reaction, it is also an energy source.
Technical Definition
Olivine generally appears in a variety of yellowish-green and yellowish-brown colors, depending on its specific chemical composition. It has a hardness of 6.5 to 7 on the Mohs scale. The name olivine refers to a series of high-temperature minerals that have the end members forsterite (Mg2SiO4) and fayalite (Fe2SiO4). When the two are chemically combined they form the magnesium iron silicate that is commonly called olivine. The higher-temperature member, forsterite, is rich in the element magnesium.
Description, Distribution, and Forms
Olivine is the group name for a series of minerals that have the end members forsterite and fayalite. The olivine group of minerals is one of the more important rock-forming minerals that make up the Earth’s crust. It is a high-temperature mineral group that is often associated with the volcanic rock basalt. It is a common mineral in the rocks that constitute the Earth’s lower crust and upper mantle. Olivine is also one of the essential minerals found in the stony variety of meteorites.
Olivine often occurs as attractive crystals. In color, olivine can appear with differing shades of yellowish-green. Depending upon its specific chemical composition, olivine can also appear in shades of yellowish-brown to an almost reddish color.
History
Forsterite was named after Johann R. Forster, an eighteenth century German naturalist who sailed with the English explorer Captain James Cook. Fayalite, the lower-temperature end member of the series, is rich in iron. It was named after the island Fayal in the Azores, where it is abundant.
Obtaining Olivine
Since olivine is a high-temperature mineral, it is usually absent from the Earth’s surface. Large deposits of olivine are often associated with certain volcanoes. An unusually explosive volcano can rapidly transport olivine up from great depths and then expel it as it erupts. Lavas produced by such volcanoes often have numerous individual olivine crystals scattered throughout; the crystals may also clump together and form as nodules. In both cases these crystals were forming within the magma at depth and were then transported upward with the rising magma. When the magma eventually flowed out of the volcano as lava, it contained the olivine that originally formed at great depth. Associated with these eruptions are other rocks called xenoliths, which also formed at depth; they contain olivine as one of their principal minerals. This kind of rock is called periodite.
Uses of Olivine
Peridot is the variety of olivine that is used as a gemstone. It is somewhat transparent and ranges in color from a yellowish-green to olive green. The dark yellow-green stones are considered to be the most valuable. Flawless peridot is common, and it can be faceted in many different ways. Fine-quality peridot comes from the San Carlos Indian Reservation in Arizona. The most sought-after stones come from the island of Zebirget in the Red Sea. Peridot is the birthstone for the month of August.
Bibliography
Natural Resources Canada.
U.S. Geological Survey.