Kimberlite

Kimberlite is a special kind of rock that comes from deep inside the Earth. It is very rare, but it is very important because it is where most diamonds are found. The name kimberlite comes from a town called Kimberley in South Africa. In 1869, a very large diamond called the Star of South Africa was found there, which started a big search for diamonds.

Kimberlite is found in tall, thin shapes called kimberlite pipes that shoot up from deep in the Earth. These pipes bring diamonds and other interesting rocks to the surface very quickly. Scientists think kimberlite forms far down in the Earth, between 150 and 450 kilometers deep, where it melts and then bursts upward.

Even though kimberlite is rare, it is very interesting to scientists. It comes from deeper in the Earth than most other rocks and has a special mix of ingredients. Studying kimberlite helps us learn more about what the deep Earth is made of and how it changes over time.

Morphology and volcanology

Many kimberlite structures push up from deep underground in a special carrot shape called a "pipes". This shape happens because of a powerful explosion caused by hot, gassy liquid rock. This gas makes the rock burst upward, creating tall columns of rock that reach the surface.

These explosions break the rock around them and bring pieces of deep Earth rock, called xenoliths, to the top. Scientists study these pieces to learn about the deep Earth. The shape of these kimberlite pipes can vary, but they often have narrow paths of rock leading down from the surface. Near the surface, the explosion creates a wide, cone-like shape that reaches up to the ground. Sometimes, the surface looks a little like a special type of volcano called a maar volcano. These kimberlite paths can be thin, while the pipes can be from about 75 meters to 1.5 kilometers wide.

Petrology

Kimberlite rocks come from deep within the Earth, and scientists are still learning about where they form and how they develop. These rocks have special minerals that tell us they formed under very high pressure and temperature deep below the surface.

Historically, kimberlites were split into two groups based on their looks. Later, they were renamed Group I and Group II using special tests. Some scientists think Group II kimberlites are so different that they might not even be closely related to Group I.

Group I kimberlites contain certain minerals like olivine and carbonate, along with others such as ilmenite, pyrope, diopside, phlogopite, enstatite, and chromite. These minerals often appear in different sizes within the rock.

Olivine lamproites used to be called Group II kimberlite or orangeite, but they are found all over the world, not just in South Africa. They have lots of water and special micas, along with olivine crystals.

Kimberlites have unique minerals like chromium diopside, chromium spinels, magnesian ilmenite, and chromium-rich pyrope garnets, which help scientists identify them because these minerals are rare in other rocks.

Geochemistry

Kimberlites have special features that make them different from other rocks formed from cooled lava. These features help scientists learn about the deep Earth where these rocks come from.

Kimberlites contain a lot of magnesium oxide, more than 12%, showing they formed deep in the Earth where magnesium-rich minerals like olivine are common. They also have high amounts of potassium oxide compared to aluminum oxide.

These rocks are rich in elements such as nickel, chromium, and cobalt, which shows they come from parts of the Earth that have not changed much.

Kimberlites also have lots of special elements called rare earth elements and other important elements like potassium, which suggests they come from areas deep in the Earth that have been changed by watery fluids.

A key trait of kimberlites is that they contain a lot of water (H₂O) and carbon dioxide (CO₂). These help carry diamonds from deep within the Earth up to the surface.

Exploration techniques

Exploring for kimberlite, the rock that often contains diamonds, uses many different methods. Scientists look for special minerals that come from kimberlite pipes. They collect samples from soil and streams to find these minerals, which helps them trace back to where the kimberlite might be.

They also use special tools to study the Earth’s surface. These tools can find areas where kimberlite might be hidden under layers of soil or rock. By putting all this information together, they can make detailed maps showing where to look next for diamonds.

Historical significance

Kimberlites help us learn about the deep parts of the Earth. By studying them, scientists understand more about how the Earth works and how hot rocks move inside the planet. Kimberlites can carry pieces from deep inside the Earth to the surface, giving us samples that are usually hard to reach.

Kimberlites are important for finding diamonds. Diamonds form deep inside the Earth, and kimberlites bring them up. When people found kimberlites with diamonds in the 1870s in Kimberley, it started a diamond rush and made the area a big place for diamond mining. Today, finding kimberlites helps people search for new diamond spots all over the world.

Kimberlites also tell us about Earth’s history, showing how continents were formed and moved over time.

Economic importance

Kimberlites are very important because they are the main source of natural diamonds. Many kimberlite pipes also hold other diamond deposits. As of 2014, around 6,400 kimberlite pipes are known on Earth, and about 900 of these contain diamonds. Mining happens at roughly 30 of these pipes.

The first kimberlite deposits were found in Kimberley, South Africa, which is where the name comes from. These deposits were tricky to find, especially in northern Canada in the early 1990s, where they were hidden under ice-covered ponds.

(See also: Mir Mine and Udachnaya pipe, both in the Sakha Republic, Russia)

Related rock types

Kimberlite is related to several other types of rocks. One is lamproite, which is mantle rock that comes to the surface through volcanic pipes. Another is lamprophyre, a type of igneous rock with lots of potassium. Nepheline syenite is a holocrystalline plutonic rock, meaning it forms from slowly cooling magma deep underground. Finally, ultrapotassic igneous rocks are a class of rare rocks that are rich in potassium and come from the Earth's mantle.