The Gemstone Andalusite
Andalusite gemstones are remarkable for their fascinating color habits and very strong
pleochroism, which can cause a muliticolored effect of shades of yellow, olive-green, and reddish-brown within a single gem. Although Andalusite as a mineral is not uncommon, the transparent variety used as a gem is very rare. Another important form of Andalusite that is entirely different is the mostly opaque
Chiastolite variety, which is known for its unique cross-shaped design within the body of a crystal.
Color
?
White, Green, Yellow, Orange, Brown, Pink, Gray, Black, Multicolored
Chemical Formula
?
Al
2SiO
5
Mineral Class
?
Andalusite
Additional Properties
|
Refractive Index
?
1.62 - 1.65 |
Double Refraction
?
-0.01 |
Transparency
?
Transparent to opaque |
SG
?
3.1 - 3.2 |
Luster
?
Vitreous |
Cleavage ?
2,1 |
All About
The strong
pleochroic effect in transparent Andalusite exhibits itself with a display of colors when viewing a gemstone through different angles. The intensity of the colors also varies by the viewing angle. The cut of an Andalusite gem plays a critical role in how the color will display itself in a cut stone. Gemstones can be cut either in a long shaped or equant shape. Long cuts will allow gemstones to show one color near the center and a different color on the ends, and equant square or round cuts will allow the multicolored effect to blend in an interesting manner.
Uses
?
Andalusite is used a minor gemstone. Although it forms hard and resistant gemstones of beautiful color, deposits of gem quality material are not extensive enough to make Andalusite into a standardized gemstone. The cross-patterned
Chiastolite variety is also used as a minor gemstone, and can be cut into rounded disc-like slices and polished.
Varieties
?
-
Chiastolite
-
Variety of Andalusite with a distinctive cross pattern (or occasionally a checkerboard pattern) that forms in the interior cross-section of a crystal.
-
Viridine
-
Bright green to olive-green variety of Andalusite, with its color supposedly caused by manganese impurities.
Treatments & Enhancements
?
Andalusite gemstones are generally not treated or enhanced.
Andalusite Sources
?
The rare gem variety comes primarily from Brazil. Chiastolite comes from many locations worldwide, including Australia, China, Portugal, Russia, Spain, and the U.S. (California and Massachusetts).
Similar Gemstones
?
Peridot and
Chrysoberyl lack the strong
pleochroism and multicolored effect
Andalusite in the Rough Photos
?