Peridotite Facts

Peridotite Facts
Peridotite is an igneous rock, hard and rough, made up mostly of the minerals olivine, pyroxene, and amphibole. It is coarse grained, dark-colored, and ultramafic, which means it has very low silica content compared to other igneous rocks though is rich in minerals. Peridotites often contain chromite, and ore of chromium, and they can be a source for diamonds, which makes them economically important. In addition, they have the potential to be used as a material for isolating carbo dioxide. A large portion of the upper part of the Earth's mantle is thought to be composed of peridotite.
Interesting Peridotite Facts:
The word peridotite comes from the gemstone peridot consisting of pale green olivine.
Different igneous rocks are considered to be a part of the peridotite family including: lherzolite, harzburgite, dunite, wehrlite, and kimberlite. Most are greenish in color.
The minerals that compose peridotite are mostly high-temperature and are unstable at the Earth's surface, quickly altered by weathering and hydrothermal solutions.
Those that are stable at the Earth's surface contain magnesium-oxide bearing minerals that can alter to form carbonates such as magnesite or calcite.
Alteration of other peridotites forms serpentinite, chlorite, and talc.
When peridotite isolates carbon dioxide into a stable solid, it occurs when the gas mixes with magnesium-rich olivine to form magnesite. The reaction happens at a geologically rapid rate.
The peridotites on the Earth's surface are thought to be rocks that have been brought up from deep-source magmas by structures such as ophiolites and pipes. It is also found in the igneous rocks of sills and dikes.
The studies of these ophiolites have helped geologists better understand the process of seafloor spreading and the formation of oceanic lithosphere.
Pipes from when a deep-source volcanic eruption brings magma up from the mantle and they are the origin for most of the Earth's diamond deposits.
The dikes and sills that are composed of peridotites are exposed by erosion providing another way for this rocks observation at the Earth's surface.
Diamonds that are delivered to the Earth's surface are in pieces of rock known as xenoliths. The formation of these diamonds take place at very high temperatures 100 miles below the surface.
Some peridotites contain significant amounts of chromite forming when a subsurface of magma slowly crystallizes.
At the early stages of crystallization, high-temperature minerals such as olivine, orthopyroxene, clinopyroxene, and chromite begin to melt. The minerals can form layers of peridotite on the bottom of the magma body, and up to 50% of the rock can be chromite.
Peridotite on the Earth's surface can be quickly obscured by soil, sediment, glacial till, and vegetation.
Peridotite often has magnetic properties significantly different from surrounding rocks and a magnetic survey can be used to locate them.
Geologists can locate peridotite bodies by prospecting for chromite, garnet, and other resistant indicator minerals. The peridotite weathers and the olivine breaks down resulting in the minerals.
Because of its potential use for isolating carbon dioxide, scientists are investigating its use to store carbon dioxide that are responsible for global warming, though it may be too costly.


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