PERIDOTITE: CHEMICAL COMPOSITION, CHARACTERISTICS AND USES - CULTURE VOCABULARY - 2025

The peridotite is the generic name given such ultramafic rocks or ultrabasic intrusive since its formation is at least 40% of the silica. They are dark in color, between greenish and black, with a dense texture and coarse grain, generally as a stratified igneous complex.

These rocks are mainly composed of olivine, which is mixed with other mafic minerals, and may or may not contain clinopyroxene and orthopyroxene. Peridotites are highly valued rocks in the market because they often contain chromite, the only chromium mineral.

Peridotite rocks

Likewise, they are found in diamond veins, since they can contain them as source rock. They can also be used as a primary material to take up carbon dioxide. Peridotites are also of great importance for geological studies of the Earth's mantle.

This importance lies in the fact that it is believed that a large part of the Earth's mantle is composed of this type of igneous rock; for this reason, peridotites are considered to be more representative of the upper mantle of the Earth than of the crust.

Chemical composition

Peridotites mostly contain a group of rock minerals called olivine (Mg2SiO4), basically forsterite and sometimes fayalite.

Olivine is present in 40% more or less in these types of rocks. It is frequently associated with other mafic minerals, such as amphiboles and pyroxenes.

Both minerals add iron (FeO) to the chemical composition of peridotites at a level greater than 7%. Peridotites have a lower silica content (+ - 40%) compared to other igneous rocks. They also contain very little feldspar and quartz.

In their chemical composition, these rocks also have a high presence of magnesium (greater than 18%), which gives it its greenish color.

On the other hand, its sodium (Na20) and potassium (K20) content is very poor. Other minerals present in peridotites but in an accessory way are spinel, garnet and chromite.

Alterable materials

The minerals that make up the mantle where the peridotite rocks are found are generally of high temperature.

When coming to the earth's surface they have an unstable behavior. They are minerals that change very quickly when exposed to the elements or hydrothermal solutions.

When disturbed, minerals that contain magnesium oxide can form carbonates, such as calcite or magnesite. These minerals are more stable when they come into contact with the Earth's surface. Other peridotite rocks when altered form chlorite, serpentinite and talc.

Peridotites can sequester carbon dioxide gas found in a geologically stable solid body.

This phenomenon is produced by combining carbon dioxide with olivine rich in magnesium, which forms magnesite. This reaction usually occurs very quickly from a geological point of view.

Magnesite, which becomes much more stable over time, serves to store carbon dioxide.

Types

Peridotite rocks contain several types of intrusive igneous rocks. This family of rocks includes: harzburgite, wehrlite, lherzolite, dunite, and kimberlite. Most of these are green in color due to their olivine content.

Harzburgite

It is basically composed of olivine and orthopyroxene, mixed with small amounts of garnet and spinel.

Wehrlite

This peridotite is mainly composed of orthopyroxene and clinopyroxene, as well as olivine and hornblende.

Lherzolite

It is composed mainly of olivine mixed with significant amounts of clinopyroxene and orthopyroxene. A large part of the Earth's mantle is believed to be made up of lherzolite.

Dunite

This peridotite is composed primarily of olivine, but can contain large amounts of pyroxene, chromite, and spinel.

Kimberlite

This type of rock is composed of approximately 35% olivine, mixed with significant amounts of other minerals; mainly carbonates, phlogopite, serpentine, pyroxenes, diopside, garnet, monticelite and garnet. Kimberlite sometimes contains diamonds.

Kimberlite-type peridotite with diamond

characteristics

- It is a type of ultrabasic igneous rock, composed mainly of olivine minerals.

- Their color ranges from greenish to black, and they have a phaneritic type texture, with coarse grains.

- Peridotites are a reservoir or store of carbon dioxide.

- They are the main rocks that make up the upper mantle of the Earth and are also found in the ophytic sequence of the oceans, at the lower level of the gabbro layer.

- These types of rocks often have magnetic properties that differentiate them from other rocks. To locate them, geologists sometimes use an aerial magnetic survey with equipment that measures their intensity.

- Peridotites are rocks that originate in the Earth's mantle and from there emerge to the surface through magmas. Researchers believe that the mantle is composed primarily of these types of rocks.

Applications

- As a store or reservoir of carbon dioxide, peridotite rocks can be used for scientific purposes. Their study allows us to establish the data of fossils, the ages of the Earth, or even climate change through the sequestration of carbon dioxide.

- They are used to study the seabed and its extension process, as well as the formation of the oceanic lithosphere. They allow a better understanding of the constitution of the Earth's mantle. These studies are carried out through ophiolites, large slabs of oceanic crust that emerge to the surface bringing large masses of peridotite.

The ophiolites include part of the displaced mantle on the continental crust at the convergent plate boundaries.

- They serve as a clue for the location of diamonds, because the diamonds that are formed in the mantle emerge to the earth's surface wrapped in peridotite rocks of the kimberlite type. This occurs when xenoliths are shed from the mantle.

Xenoliths are pieces of rock that are found in the interior of the Earth and are detached from the mantle and the walls of the pipe. This process occurs through the pipes that are formed with volcanic eruptions.

- They are of great economic importance because they contain chromite, which is the main source of chromium.

References

1. Peridotite. Retrieved May 24, 2018 from geology.com
2. Peridotite. Consulted from mindat.org
3. Peridotite. Consulted of sciencedirect.com
4. Peridotite, characteristics, origin, texture, uses, composition, minerals. Consulted of geologiaweb.com
5. Olivino. Properties, uses, composition. Consulted of mineralsyrocas.com