Peridotite

This rock is called peridotite.

It is very heavy and dense. It is mostly green.

This color comes from tiny green parts inside it. This rock lives deep inside the Earth. It makes up a large part of the mantle. Some pieces come up to the surface in volcanoes. These pieces can even hold diamonds!

It is a special piece of our world.

Peridotite is a very heavy rock. It is the main rock of the Earth's upper mantle. The mantle is the thick layer below the crust.

This rock is mostly made of two minerals. They are called olivine and pyroxene. Olivine is often a bright green color. This is why the rock is usually green too. The name peridotite comes from the peridot gemstone. A peridot is a pale green stone made of olivine.

Peridotite has many different types. One type is called dunite. Dunite has more than 90% olivine. Another type is called kimberlite. Kimberlite forms in volcanic pipes. It is the rock that holds diamonds!

We can find peridotite in a few ways. Sometimes, volcanoes bring pieces up from deep down. These pieces are called xenoliths. They help scientists study how the Earth formed. Other times, pieces of the mantle move onto land. This can happen when continents crash together. These pieces are called ophiolites.

Peridotite is a very heavy and dense rock. It is the main rock found in the upper part of the Earth's mantle. The mantle is the thick layer located beneath the Earth's crust.

This rock is called ultramafic. This means it has very little silica, which is a common mineral in many other rocks. Instead, it is very high in magnesium and iron. Because it has so much magnesium, it contains a lot of the mineral olivine. This mineral often gives the rock a bright green color.

This rock works by forming deep inside the Earth. It can form as solid blocks or as crystals that grow from magma. Magma is hot, liquid rock found in the mantle.

When these crystals grow and pile up, they create different types of rock. Some types, like dunite, form when olivine crystals settle on the floor of a magma body. This happens as the magma cools down very slowly. Other pieces move toward the surface through volcanic pipes. This process can bring pieces of the deep mantle up to where we can see them.

Scientists study these rocks to learn about the past. Some peridotite pieces are found in special volcanic rocks called kimberlite. Kimberlite is the rock that holds diamonds.

These pieces are called xenoliths, which means "foreign stones." They are brought up from depths of 30 km to 200 km or even more. By looking at the elements inside them, like osmium, researchers can find clues about how the Earth was formed. They can even learn about the early composition of the mantle.

There are many different names for peridotite based on what is inside it. Dunite is a type that is more than 90% olivine. Harzburgite is another type that makes up much of the mantle. There is also lherzolite, which is thought to make up much of the upper mantle.

Some peridotites also contain a mineral called hornblende. This happens when fluids change the rock. Other minerals like chromite, garnet, or spinel can also be present. These minerals help scientists estimate how deep the rock was formed.

Peridotite is hard to find on the surface of the Earth. This is because olivine reacts quickly with water. When it touches water, it can change into a different green mineral called serpentine.

This change can make the rock look yellow or even brown. You might also see pieces of the mantle on land in mountain belts. These pieces are called ophiolites. They move onto continents when land masses collide. This brings deep Earth secrets right to our doorstep.

Peridotite is a dense, coarse-grained igneous rock. It is the dominant rock of the Earth's upper mantle. This layer lies beneath the crust. Peridotite is classified as ultramafic. This means it contains less than 45% silica. It is very rich in magnesium and iron.

Most of its magnesium is found in the mineral olivine. This mineral often gives the rock a bright green color. The name peridotite actually comes from the gemstone peridot. This gem is made of pale green olivine.

Peridotite forms deep within the Earth's mantle. It can form as solid blocks or fragments. It can also form as crystals that accumulate from magma. Magma is liquid rock found in the mantle. As magma cools, crystals can settle and pile up. This process creates different types of rock layers. Some rocks form as cumulates. These are layers where crystals have gathered on the floor of a magma body.

Other pieces reach the surface through volcanic pipes. This process brings deep mantle samples to the surface.

Scientists classify peridotite by its mineral proportions. The main minerals are olivine, pyroxene, and hornblende. Peridotite must contain at least 40% olivine. If the pyroxenes make up more than 60%, the rock is called a pyroxenite. There are several specific types of peridotite. Dunite is a type with more than 90% olivine. It often contains chromite.

Harzburgite is another type. It has less than 5% clinopyroxene. Wehrlite is a third type with less than 5% orthopyroxene. Lherzolite is an intermediate type. It is thought to make up much of the upper mantle.

Other rare types exist based on different mineral mixes. Kimberlite is a rare, broken-up variant of peridotite. It forms in volcanic pipes and hosts diamonds. Hornblende peridotite is also found. This type forms when fluids change the original mantle rock. Pyroxene hornblende peridotite is an intermediate version of this. These rocks are often found as xenoliths. A xenolith is a "foreign stone" trapped in another rock. They are found in rocks like basalt or andesite. These stones provide a window into the deep Earth.

Peridotite is vital for understanding Earth's history. Some nodules are found in diamond-bearing kimberlite. These samples come from depths of 30 km to 200 km or more. They preserve isotope ratios of osmium and other elements. These ratios record processes from when Earth was formed. Paleogeologists use these clues to study the early mantle. Other minerals help estimate formation depth. For example, plagioclase appears at shallow depths. Spinel appears between 20 km and 60 km. Garnet appears below 60 km. This helps scientists map the deep interior.

Peridotite is rarely seen at the Earth's surface. It is highly unstable when exposed to water. Olivine reacts quickly with water at typical temperatures. This process turns olivine into a mineral called iddingsite.

This can change the rock's color to brown or yellow. Many surface rocks are actually serpentinite. This forms when pyroxene and olivine turn into green serpentine. This reaction increases the rock's volume. It also makes the rock mechanically weak. This allows the rock to flow easily within the Earth.

We can find pieces of the mantle on land through special processes. Oceanic plates usually sink into the mantle at subduction zones. However, sometimes they are pushed onto continents instead. This process is called obduction. These pieces of oceanic lithosphere are called ophiolites. They consist of peridotite and other rocks like gabbro and basalt. These ophiolites can be found in mountain belts. They are often called alpine or orogenic peridotite massifs. They show us what the ocean floor looks like deep underground.