A xenolith is a piece of rock trapped in another type of rock.

Most of the time, a xenolith is a rock embedded in magma while the magma was cooling. Magma is the molten rock beneath the Earths crust that emerges as lava during a volcanic eruption. The rock that forms from cooled magma is called igneous rock. Xenoliths are different types of rock embedded in igneous rock.

Xenoliths are torn from deep cracks, or pipes, in the Earths surface. Magma rises to the Earths surface through these pipes between the Earths crust and mantle. As the molten material rises, it tears off bits and pieces of the magma pipe in which it is traveling. These bits and pieces, trapped in the magma but not melting into it, become xenoliths. Crystals that are torn from the sides of magma pipes are called xenocrysts.

As magma erupts or flows from the Earths surface, it is cooled by exposure to air or water. Lava cools fairly quickly, and various types of igneous rocks are formed. Xenoliths are usually visible. They have a different color and density than the surrounding igneous rock. Xenoliths can be as small as a grain of sand or as large as a football, and as long as several meters.

Xenoliths and xenocrysts are affected by temperature. A xenolith may lose its unique qualities if it melts into the surrounding magma. As it cools, the material may cease being a xenolith at all and become a metamorphic rock. Metamorphic rock is rock that has changed from one form (sedimentary or igneous) to another.

Xenoliths and xenocrysts are often identified by the names of the two rock types involved. A peridotite xenolith in a basaltic lava flow, for instance, means a chunk of the rock peridotite is embedded in basalt rock. The peridotite is usually yellow and dense, while the basalt is usually grey and light.

Xenoliths and xenocrysts provide valuable information about the geology of the Earths mantle. Scientists study the chemical properties of xenoliths to understandthe depth at which they were formed. Many xenocrysts were created hundreds of kilometers within the Earth, far below the deepest mines and wells. The information about the condition of the mantle at these depths would be impossible to understand without xenoliths and xenocrysts. Some of the features studied by geologists are temperature, pressure, construction, and movement within the Earth's surface.

Xenoliths can be a piece of rock trapped in a piece of sedimentary rock, but this is rare. Xenoliths have also been found in meteorites, or rocks from outer space that have crashed into Earth. The xenoliths in meteorites were formed from collisions with other objects outside the Earths atmosphere.

xenolith
A xenolith is a rock trapped inside another rock.

Xenocrysts are a Girl's Best Friend
Diamonds are formed in the Earth's upper mantle. A type of igneous rock called kimberlite is known for carrying xenocrysts of diamonds to the surface, where they can be mined. Kimberlite was named after the rich Kimberley mine in South Africa, where a diamond rush began in 1871.

Noun

layers of gases surrounding a planet or other celestial body.

basalt
Noun

type of dark volcanic rock.

cease
Verb

to stop or end.

chemical property
Noun

unique identity of a substance expressed by its type and arrangement of molecules.

collision
Noun

crash.

construction
Noun

arrangement of different parts.

Noun

rocky outermost layer of Earth or other planet.

crystal
Noun

type of mineral that is clear and, when viewed under a microscope, has a repeating pattern of atoms and molecules.

Noun

number of things of one kind in a given area.

diamond
Noun

type of crystal that is pure carbon and the hardest known natural substance.

Noun

our planet, the third from the Sun. The Earth is the only place in the known universe that supports life.

embed
Verb

to attach firmly to a surrounding substance.

emerge
Verb

to develop or come into view.

eruption
Noun

release of material from an opening in the Earth's crust.

geology
Noun

study of the physical history of the Earth, its composition, its structure, and the processes that form and change it.

igneous rock
Noun

rock formed by the cooling of magma or lava.

kimberlite
Noun

type of magma or igneous rock associated with diamonds.

lava
Noun

molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.

Noun

molten, or partially melted, rock beneath the Earth's surface.

magma pipe
Noun

channel that transports molten rock to the surface from very deep volcanoes.

Noun

middle layer of the Earth, made of mostly solid rock.

metamorphic rock
Noun

rock that has transformed its chemical qualities from igneous or sedimentary.

Noun

type of rock that has crashed into Earth from outside the atmosphere.

mine
Verb

to extract minerals from the Earth.

molten
Adjective

solid material turned to liquid by heat.

peridotite
Noun

type of igneous rock

pressure
Noun

force pressed on an object by another object or condition, such as gravity.

sedimentary rock
Noun

rock formed from fragments of other rocks or the remains of plants or animals.

xenocryst
Noun

crystal embedded in an igneous rock.

Noun

piece of rock embedded in another type of rock, usually igneous.