Xenolith!

XENOLITH

it is rock fragment which becomes enveloped in a larger rock during the latter's development & hardening. in geology xenolith is almost used to describe igneous rock during magma emplacement & eruption. xenolith may be engulfed along the margins of magma chamber, torn loose from the walls of an erupting lava conduct / explosive diatreme along the base of a flowing lava on earth's surface. xenolith provide information about the composition of the innacessible mantle, basalts, kimberlites, lamproites which have their source in the upper mantle. often contain fragments & crystals assumed to be a apart of the originating mantle minualogy.