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Gemstones 250x250

The Gemstone Andalusite

Large Emerald-Cut 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

Hardness

? 7 - 7.5

Chemical Formula

? Al2SiO5

Mineral Class

? Andalusite

Additional Properties

Crystal System
? Orthorhombic
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 Photos

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Andalusite in the Rough Photos

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