1/4/2024 0 Comments Olivine meteorite![]() Olivine is the name given to a group of silicate minerals that have a generalized chemical composition of A 2SiO 4. Photograph by Siim Sepp, used here under a Creative Commons License. If you think the grains have a "gemmy" appearance, olivine is the mineral name of a gemstone known as "peridot." The width of this view is about 10 millimeters. The white grains are coral fragments, and the gray-black grains are pieces of basalt. Olivine sand: Green olivine sand from Papakolea Beach, Hawaii. Because it is so easily altered by weathering, olivine is not a common mineral in sedimentary rocks and is only an abundant constituent of sand or sediment when the deposit is very close to the source. Olivine is one of the first minerals to be altered by weathering. When olivine is metamorphosed, it is transformed into serpentine. The dolomite contributes magnesium, and silica is obtained from quartz and other impurities in the limestone. This concentrated accumulation of olivine can result in the formation of olivine-rich rocks such as dunite in the lower parts of a magma chamber.Ĭrystals of olivine are sometimes formed during the metamorphism of a dolomitic limestone or dolomite. During the slow cooling of a magma, crystals of olivine may form and then settle to the bottom of the magma chamber because of their relatively high density. That makes it one of the first minerals to crystallize from a magma. Olivine has a very high crystallization temperature compared to other minerals. These types of rocks are most common at divergent plate boundaries and at hot spots within the centers of tectonic plates. It usually crystallizes in the presence of plagioclase and pyroxene to form gabbro or basalt. Most olivine found at Earth's surface is in dark-colored igneous rocks. The gem on the right is a 1.96 carat cushion checkerboard cut peridot of about 10 x 8 millimeters from China. The gem on the left is a 1.83 carat cushion cut peridot of about 8 x 6 millimeters from Myanmar. These two faceted stones are nice specimens of yellowish green peridot. Olivine gemstone: The gemstone known as peridot is a variety of olivine.
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