A mantle xenolith is a fragment of the Earth’s mantle that is brought to the surface by volcanic activity, typically enclosed within an igneous rock. These xenoliths provide direct evidence of the composition, temperature, and pressure conditions in the mantle and are crucial for understanding mantle processes and Earth’s interior.
Reference: Harte, B. (2010). “Mantle Peridotites and Processes—The Kimberlite Sample.” Journal of the Geological Society, 167(4), 639-646.