Xenoblast:
A crystal that has grown in a rock during the process of metamorphism and which has not developed its characteristic crystal faces because of space limitations.
Xenolith:
A preexisting rock that has been incorporated into magma without melting. When the magma crystallizes the preexisting rock fragment is known as a xenolith.
Xerophyte:
A plant that can survive in a very dry location or climate.
X-ray Diffraction:
A technique used to identify minerals by bombarding them with X-rays. Planes of repetition within the atomic structure of the mineral diffract the X-rays. The pattern of diffraction is unique for each mineral structure and can be used for identification.