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Chemical Formula | (Na,Ca)1-2Si3-2O8 | ||||
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Composition | Sodium calcium aluminum silicate. The ratio
of sodium to calcium is about 7:3. The amount of aluminum
atoms are between 1 and 2, and the amount of silicon
atoms are between 3 and 2. In the Plagioclase Feldspar series, Labradorite contains between 30 and 50 percent Albite (Ab), and between 50 and 70 percent Anorthite (An). |
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Color | White, gray, light blue, light green, pale
orange-red, black, usually with a strong display of
purple, blue, and green schillers. A Scandinavian variety, known as Spectrolite, shows the Schiller effect with intense reds, oranges and yellows as well as blues and greens. |
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Streak | White | ||||
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Hardness | 6 - 6½ | ||||
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Crystal Forms and Aggregates |
(Triclinic) Labradorite rarely forms in crystals. When it does, they are generally tabular and usually twinned. Most commonly occurs massive, grainy, as elongated fragments, as chunky masses, and rounded. | ||||
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Transparency | Transparent to translucent | ||||
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Specific Gravity | 2.69 - 2.72 | ||||
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Luster | Vitreous to pearly | ||||
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Cleavage | 2,1 - basal ; 2,1 - prismatic ; 3,1 -
pinacoidal The cleavage angle is about 90º |
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Fracture | Conchoidal to uneven | ||||
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Tenacity | Brittle | ||||
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Varieties |  Spectrolite - Scandinavian
variety displaying a schiller effect with intense reds, oranges
and yellows as well as blues and greens. |
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In Group | Silicates ; Tectosilicates ; Feldspar group ; Plagioclase Feldspars | ||||
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All About | Labradorite belongs to the Plagioclase
Feldspar group, an isomorphous solid solution series. Albite is one end member, containing
sodium and no calcium. The other end member, Anorthite, contains calcium and no sodium.
The intermediary members are Oligoclase, Andesine, Labradorite, and
Bytownite. Labradorite is an unusual mineral. Its displays an iridescent play of colors, caused by internal fractures in the mineral that reflect light back and forth, dispersing it into different colors. This effect, known as labradorescence, gives Labradorite its appeal and fame. Specimens sold to collectors are usually polished or sliced by dealers to fully bring out this phenomenon. Sliced slabs are sometimes sold by dealers in water, which enhances the effect. |
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Uses | Labradorite is a very popular mineral, and it makes a unique gemstone. It is cut and polished into cabochons and beads. Some exquisite ornaments are carved out of large Labradorite chunks. | ||||
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Striking Features | Play of color, hardness, cleavage, and crystal forms | ||||
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Popularity (1-4) | 2 | ||||
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Prevalence (1-3) | 2 | ||||
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Demand (1-3) | 1 | ||||
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Distinguishing Similar Minerals |
Labradorite is easily distinguished from all minerals. However, specimens that don't exhibit labradorescence may be confused with many minerals, especially other feldspars. | ||||
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Commonly Occurs With |
Quartz, Muscovite, Biotite, Hornblende, Augite | ||||
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Noteworthy Localities |
The finest Labradorite comes from Finland and Russia. Deposits containing labradorescent material also exist in Romania, Madagascar, and New South Wales, Australia. Famous deposits are in Canada in Labrador (Nain, Tabor Island) and Newfoundland. The U.S. also contains a number of deposits, but only few labradorescent specimens come from them. The most famous U.S. locality is the Adirondack Mountains of upstate New York, with Saranac Lake being the most productive of the occurences there. A clear, transparent form of Labradorite is found in Millard Co., Utah. | ||||
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Picture Icon Links |
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Picture Links | 1. "Spectrolite" 2. Polished Specimen |
