Xalostocite

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

Xenolith

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

Xyloid jasper

Xyloid jasper is jasperized wood (petrified wood). It is wood that has fossilized - all the original chemicals have been replaced with minerals, making a stone-like replica of the original wood.