xenocrystalline

Xenocrystalline is an adjective used in geology to describe crystals within a rock that originate from a source outside the rock's own crystallization history. The term derives from the Greek xenos, meaning foreign or strange, and krystallos, meaning crystal. A xenocrystal is a single foreign crystal, while xenocrystalline describes a rock texture containing such grains.

In igneous rocks, xenocrystals form when a magma assimilates crystals from surrounding country rock or from older intrusions, leading to mixed or contaminated mineral assemblages. They may also persist in mantle-derived magmas as crystallization proceeds around them. In metamorphic rocks, xenocrystalline grains can reflect earlier protoliths or events from which they were inherited. In meteorites, xenocrystalline grains indicate incorporation of material from different bodies or fragments during solar system processes.

Identification relies on mineralogy, age, and chemistry. Xenocrystals often show discordant crystallization ages or compositional signatures relative to the host rock and may occur as isolated grains or as coarse inclusions. When studied, they illuminate processes such as magma mixing, crustal contamination, and the thermal history of rocks. Their presence helps geologists reconstruct the interactions between magmas and surrounding rocks, as well as the history of material exchange in planetary contexts.

See also: xenolith, xenocryst, xenolitic.