Xalostocite
Xalostocite is a pink grossular garnet that is found in a matrix of white marble. Xalostocite is found in Xalostoc, Mexico.

Xenolith
A xenolith (also called an inclusion) is a fragment of foreign rock that is embedded inside an igneous rock.

Xyloid Jasper
This is petrified wood that consists mostly of jasper. The original chemicals are replaced with minerals leaving a replica of the original wood in stone. See Palmwood.