Minerals (Category B)
Andalusite is named for its type locality of Andalusia, Spain. It is a polymorph with two other minerals: kyanite andsillimanite. A polymorph is a mineral that shares the same chemistry but a different crystal structure with other minerals.
A unique variety of andalusite is called "chiastolite". It contains black or brown clay and/or carbonaceous material (often graphite) inclusions in the crystal. These inclusions are arranged in regular symmetrical shapes - especially prized when they are in the form of a cross or X.