Xenolith

A xenolith is a piece of rock that gets stuck inside another rock when it forms. Think of it like a piece of cookie getting caught in a cake while it’s being baked. Scientists use the word xenolith to describe pieces of rock found inside molten rock, called igneous rock. These pieces can get caught when hot, moving rock, called magma, pushes up through the Earth’s crust. They might get pulled in from the sides of a magma chamber, torn from the walls of a volcanic pipe, or picked up from the ground as lava flows.

A xenocryst is a single crystal trapped inside the rock, like a tiny gem in glass. For example, you might find quartz crystals in lava that doesn’t usually have quartz, or even diamonds inside special rocks called kimberlite.

Xenoliths are important because they help scientists learn about parts of the Earth we can’t see, like deep below the surface. Rocks such as basalts and kimberlites often carry pieces from deep inside the Earth. By studying these trapped pieces, scientists can find out more about what the Earth is made of deep down. The type of minerals in a xenolith can show how deep it came from—whether it was near the surface or much deeper.

Examples

Xenoliths can be found in many places around the world. For example, they appear in granodiorite in the Alta Stock in Little Cottonwood Canyon, Utah. There is also a large xenolith of sandstone in the Fairlee Pluton in Vermont. In Germany, peridotite xenoliths have been found within volcanic bombs from Vulkaneifel.