Xaga is a type of obsidian found in California, USA.
Xalostocite is a pink grossular garnet that is found in a matrix of white
marble. Xalostocite is found in Xalostoc, Mexico.
A xenolith (also called an inclusion) is a fragment of foreign rock that
is embedded inside an igneous rock.
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.