 : Labradorite
Labradorite & Spectrolite used in Jewelry
Source: Canada, Finland, Labrador, Madagascar, Mexico, Russia
Labradorite (aka: spectrolite, Labrador feldspar, opaline feldspar, or "black moonstone") derives its name from the principal location that it is found, Paul's Island Labrador, a region of Atlantic Canada near the island of Newfoundland. Labradorite is a semi-transparent to translucent member of the feldspar group (plagioclase feldspar - calcium sodium aluminum silicate) that occurs in crystalline masses, and occasionally in tabular crystals. Labradorite is a major constituent of medium to low silica metamorphic and igneous rocks such as andesite, basalt, diorite, and olivine gabbro.
A distinct characteristic of labradorite is its iridescent play-of-color known as the schiller effect, or "labradorescence," which occurs along internal cleavage surfaces. The schiller effect is caused by light being scattered from thin perthitic lamellar intergrowth layers of different feldspars that chemically separated (miscibility) during the cooling process. Specimens that display the schiller effect are usually cut en cabochon or as a flat plane.
Labradorite's principal base color is blue, but it can occur in a wide variety of colors such as green, orange, red, and yellow. There are gemstone varieties from Madagascar and transparent varieties from India. There is also a variety of Labradorite from Mexico that can be faceted.
Gemstone varieties from Finland that have a high amount of iridescence are sometimes referred to as "spectrolite." Other orthoclase feldspar gemstones that exhibit the schiller effect are moonstone and sunstone. Labradorite crystallizes in the triclinic crystal system with a massive crystal habit, and crystal twinning is common. Cleavage is in three directions, two of which form nearly right angle prisms. is found in association with biotite, hornblende and pyroxene.
Labradorite Crystallography, Chemistry, Physical Properties
Labradorite Optical Properties
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