...iridescent labradorescence

Labradorite (lab-ruh-daw-rahyt) is a truly beautiful minerial whose iridescence and virteous luster may be overlooked if not viewed from the proper position. As a translucent type of Feldspar, Labradorite displays strong iridescence when viewed from different angles. The Feldspar family is a fairly large group and makes up the greatest percentage of minerals found in the Earth's crust. Moonstone and Sunstone are from the same family and exhibit the same kind of translucent iridescence.

Labradorite is often thought to be a dull grey to smoky black stone with no special virtue, until the colorful "fire" is observed glowing on the surface. The colorful play of light seen dancing on the surface of this gemstone is appropriately called labradorescence or shiller.

The "fire" can range in color from intense blues and violets through to greens, yellows and oranges. The unique color display comes from light refraction on intergrowths inside the crystal. Intergrowths develop when chemically compatible elements at high temperatures become incompatible at lower temperatures causing micro-seperation of layer deep within the the crystal structure.

The color play is caused when a ray of light enters the crystal and is refracted back and forth between the inner layers. This ray of light is slowed by the refraction and produces an exiting ray of light that has a different wavelength than when it entered. The altered wavelength we see cooresponds to the wavelength of a particular color, such as blue. The "fire" effect depends on the thickness and orientation of the layers. If the layers are too thick or too thin little or no fire can be seen. The quality of Labradorite is determined partly by the color of the stone but primarily by the amount of "fire" reflected. Labradorescence is a unique mineralogical experience that must be seen in person to be truly appreciated.

The name of this gemstone is derived from the main and original source of the Canadian variety of this Feldspar stone, Labrador. The specific geological area Labradorite is found is on Paul's Island near the town of Nain in Labrador, Canada. Labradorite is also found in India, Madagascar, Newfoudland and Russia. Spectrolite, the most valued type of Labradorite, comes from Finland. Finnish Spectrolite exhibits vivid colors of bright aqua, golden yellow, peacock blue, reddish oranges, greens and reds.

Lore:
It has been told that the "god of the mines" picked Diamond and Labradorite as the "Gems of Winter" because they both display all colors of the universe. In fact, both of these gemstones combine and refract all colors of light, in contrast to all other known gemstones. Labradorite typifies the winter sun as the gem of light, it is the color of ice, like icicles sparkling in winter, or like the stars on a winter night.
Labradorite is a tremendously spiritual stone.

Sources:
http://www.galleries.com/minerals/silicate/labrador/labrador.htm
http://www.bernadine.com/gemstones.spectro.htm