Many gemstones varieties look alike, especially to the untrained observer. Given a collection of light blue colored stones -- such as topaz, aquamarine, zircon, sapphire, apatite and fluorite -- even many people in the gem trade would have a hard time identifying each variety without the use of some gemological tools.
But there are some gemstones that have such a unique look that it's hard to confuse them with any other gems. Andalusite is a good example. Andalusite has such a distinctive combination of colors, and such pronounced pleochroism, that only unusually colored tourmaline could ever be mistaken for andalusite.
Pleochroic gems appear to have different colors or depth of color when viewed from different angles. The effect is caused by differing absorption of light rays in doubly refractive crystals. Among the gems that are strongly pleochroic are andalusite, iolite, kyanite, kunzite, sphene and unheated tanzanite. Some pleochroic gems are said to be dichoric -- displaying two different colors; kunzite is an example. Others are said to be trichroic, such as andalusite.
Andalusite displays shades of yellow, olive and reddish brown depending on the orientation of the crystal. The pleochroic effect can be enhanced by specific orientation and cut. Those cuts with a long axis such as an oval, pear, marquis or emerald cut tend to show one color near the center and a second, usually darker color near the ends. Square and round cuts usually blend the colors into a mosaic.
Andalusite is usually classified as one of the lesser-known gemstones. Transparent material of gemstone quality is rare, so you are unlikely to find andalusite in your local jewelry store. It has mostly been a collector's stone but some jewelry designers have begun to incorporate it in their designs.
Andalusite deposits are found in Australia, Brazil, Canada, Russia, Spain, Sri Lanka and the USA.