Xenoliths

Part of speech: noun

Definitions

1. A type of rock fragment that becomes incorporated into a larger rock formation, often differing in composition and origin
2. Geological fragments of pre-existing rocks found within an igneous rock, indicating diverse geological processes
3. Pieces of rock from one geological setting embedded within another, often providing insights into the Earth's crust and its history

Etymology: "Xenoliths" is the plural of "xenolith", a term for a rock fragment that has been carried into a larger body of igneous rock, usually lava or magma, and is foreign to it. The word is built from two Greek elements: "xenos", meaning "stranger" or "foreigner", and "lithos", meaning "stone". Put together, the name is literally a "stranger stone," which describes exactly what a geologist finds when a fragment of older country rock is trapped inside a younger flow. The first element, "xeno-", appears in other scientific coinages where something alien or external is involved, such as "xenophobia" (fear of strangers) and "xenon", the gas named for its rarity as something "foreign" in the air. The second, "-lith", is the common scientific suffix for stone, found in words like "monolith" and "megalith". Because the word is a modern technical formation, it was assembled from these classical building blocks by geologists rather than used by the ancient Greeks, who had no concept of a xenolith.