|Andalusite is one of there gem materials with identical formulas. Andalusite, kyanite, and sillimanite all share the same chemistry and all have gemstone potential. They are polymorphs which are formed from he same material but at different temperatures and pressures.
Andalusite gets its name from it early locale, Andalusia, Spain.
Andalusite shows strong pleochroism with two distinct colors, usually a yellow-green and a rich brown. The stones are often oriented to display both colors through the crown and this give gem quality andalusite a very distinctive look. It tends to flash both the brown and yellow-green when moved in the light.
The gem has achieved more than just collector status but it is still rare in most jewelry. Sizes are usually small in the 1-3 ct. range.
Chiasrolite is another name given to the opaque variety of andelusite and it too is very unique. It has also been called "cross stone" because it produces a dark "X" when the crystals are cut in cross section. It tends to be softer than the gem variety with a hardness of around 5.5 - 6. Chiastolite gets its name from the Greek "chiastos" meaning x-marked. It was used as a cross and a means of identification for early Christians.