xenocryst

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A crystal foreign to the igneous rock in which it occurs.

Century Dictionary and Cyclopedia

1. n. In petrography, a term proposed by Sollas for a crystal in an igneous rock which has been included by the igneous magma before the solidification of the rock.

Wiktionary

1. n. a crystal that does not occur in a specific igneous rock