Xalostocite is a pink grossular garnet that is found in a matrix of white marble.
A xenolith (also called an inclusion) is a fragment of foreign rock that is
embedded inside an igneous rock.
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.