xenolith

noun

A rock fragment foreign to the igneous mass in which it occurs.

noun

In petrography, a term proposed by Sollas (1894) for a rock inclosed in an intrusive rock, and not derived from the igneous magma.

noun

any piece of rock having a different origin to that of the igneous rock in which it is found

noun

(geology) a piece of rock of different origin from the igneous rock in which it is embedded