Gemstone Series: Andalusite

Andalusite is an aluminum silicate mineral (Al2SiO3). Two minerals with the same composition but different structure (polymorphs) as andalusite are kyanite and sillimanite. Andalusite is one of my personal favorite gemstones because it is generally brown in color (there aren’t too many brown gemstones and I love to wear brown!) and it exhibits a property called pleochroism – it appears different colors from different directions. Andalusite can appear orange, green, or brown (all colors that I love to wear!), depending on what direction you view it from.

The transparent variety of andalusite that I use in my jewelry is somewhat uncommon. The opaque variety is more common, and it is often known as cross stone or chiastolite. When viewed down the c-axis, it displays a cross. This stone can be quite striking when cut en cabochon.

Andalusite has a hardness of about 7 1/2 on Moh’s hardness scale, but it is fairly brittle (easy to break). Andalusite is a metamorphic mineral, which occurs in schists, gneisses, and placers. Deposits are found in Australia, Brazil, Canada, Russia, Spain (Andalusia), Sri Lanka, and the US (Schumann, Gemstones of the World).

There is a dark green variety of andalusite called viridine, which contains iron and manganese.

Google image results for andalusite.
Andalusite entries on webmineral and mineral galleries.