When rocks are exposed to certain conditions, such as heat or pressure, they undergo a metamorphosis. This changes them into a different kind of rock, with slightly different properties than before. Some rocks can be changed into several different types of other rocks with metamorphosis. Serpentinite and soapstone, two types of rock, share the same parent stone.
Peridotite Properties
Peridotite consists mainly of the mineral olivine, according to the USGS Cascades Volcano Observatory website. Olivine contains iron and magnesium and is usually green and glassy-looking. Peridotite ranges in shade from green to brown to gray or black. Peridotite's texture is coarse and crystalline. The substance is usually dense. In gem form, peridotite becomes peridot. The American Museum of Natural history notes that peridotite, being a xenolith, can occasionally contain diamonds. In addition, peridotite can also contain garnets.
Types of Peridotite
Several different types of peridotite exist. One type of peridotite is known as lherzolite. Lherzolite forms most often in the upper mantle of the Earth's crust, including ocean floors, according to the American Museum of Natural History. Another peridotite type is harzburgite. Harzburgite consists of more olivine than lherzolite, as well as less orthopyroxene and clinopyroxene. Dunite, another form of peridotite, consists almost entirely of olivine, according to the Geological Sciences Department at Cal Poly Pomona.
Locations of Peridotite
The Earth's mantle is composed mostly of peridotite, according to the American Museum of Natural History. Cal Poly Pomona's Geological Sciences Department notes that peridotite occurs within four different geological areas: combined with other rocks of similar composition in masses, in volcanic pikes, within rocks with high potassium and sodium composition and in alpine-type mountain belts. Friends of Edgewood Natural Preserve explains that when tectonic plates beneath the sea encounter each other, one edge of a plate goes under the other plate. This then pushes sediment up and rocks form, including peridotite.
Metamorphosis
Peridotite can morph into other rock types with a metamorphosis process. This process occurs when peridotite is exposed to heat, pressure or chemical fluids, according to Georgia Perimeter College. After exposure to one of those factors, peridotite becomes one of two different types of rock. The first is serpentinite. Serpentinite is a dense, dark green rock that can contain asbestos. Soapstone, also known as steatite, is a rock that is also formed from peridotite. This rock is created with slightly more water than serpentinite, making soapstone softer. Soapstone contains talc and chlorite, which can make the rock feel slippery.
Air Purifying Benefits
In 2008, it was discovered by Columbia University doctoral student Sam Krevor that peridotite absorbs carbon dioxide. According to the Miller-McClune online magazine, the process of testing ultramafic rock for the potential to heat-trap carbon dioxide began in 2003. Peridotite was found to be both fast and efficient at carbon dioxide removal. This proves to be valuable to researchers because the rock can be used in removing air emissions at a faster rate than they are being expelled. A downside, however, is that storing the carbon dioxide could become difficult to do.
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