Labradorite is known for its remarkable iridescence. This schiller or metallic luster can be seen when light hits the stone from particular angles. Most typically, these metallic tints are violet, blue and green. This effect is so unique to labradorite that it is referred to as labradorescence. The labradorescent effect is believed to be due to the presence of very fine platelets of varying composition as well as minute inclusions of limenite, rutile and possible magnetite, which cause the diffraction of light.
Some rare specimens of labradorite display a full spectrum of colors, not only violet, blue and green; but also yellow, orange and red. These rare specimens have been given the name spectrolite. The name was introduced by the Finnish geologist Aarne Laitakari (1890-1975), former director of the Geological Survey of Finland. Laitakari's son, Pekka, discovered the first spectrolite deposit at Ylämaa in South-Eastern Finland near the Russian border while building the Salpa Line fortifications there in 1940.
The quarrying of spectrolite began after the Second World War and has become a significant local industry. In 1973, the first workshop in Ylämaa began cutting and polishing spectrolite for gemstones and jewelry.
Spectrolite and labradorite belong to the plagioclase feldspar group, a series of mixtures of sodium and calcium aluminum silicates. Other members of the plagioclase group include sunstone and andesine. Labradorite has a hardness of 6 to 6.5 on the Mohs scale and a specific gravity of 2.69 to 2.72.
Labradorite was named after the Labrador Peninsula in Eastern Canada where it was first found, in around 1770. Other labradorite deposits have been found in Australia, Finland, Madagascar, India, Mexico and the Adirondack Mountains in the United States. To date, the rare variety called spectrolite has only been found in Finland and the name has been reserved for uniquely colorful spectrolite from the Ylämma region.
- First Published: March-08-2010
- Last Updated: October-03-2014
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