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Labradorite Slab

The Mineral labradorite

Labradorite is an unusual mineral. It can display a beautiful 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 effect. Sliced slabs are sometimes sold by dealers in water, which enhances the effect.

Labradorite belongs to the Plagioclase Feldspar group, an isomorphous solid solution series. Albite is one member, containing sodium and no calcium. The other end member, Anorthite, contains calcium and no sodium. Labradorite is an intermediary member of this series. Labradorite is considered by some authorities as a variety of Anorthite rather then a separate mineral. The acclaimed Dana's System of Mineralogy lists Labradorite as an individual mineral, whereas the IMA does not recognize it as individual mineral species, but rather a sodium-rich variety of Anorthite.

For additional information, see the gemstone section on Labradorite.
Chemical Formula (Ca,Na)Al1-2Si3-2O8
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).
Color White, gray, light blue, light green, pale orange-red, black, usually with a strong multicolored display of purple, blue, and green schillers. A variety from Finland known as Spectrolite, shows the Schiller effect with dark reds, orange, yellow, blues and green color flashes.
Streak White
Hardness 6 - 6.5
Crystal System Triclinic
Crystal Forms
and Aggregates
Labradorite rarely forms in crystals. When it does, they are generally tabular and often twinned. Most commonly occurs massive , grainy , as elongated fragments, as chunky masses, and rounded.
Transparency Transparent to translucent
Specific Gravity 2.69 - 2.72
Luster Vitreous to pearly
Cleavage 2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal. The cleavage angle is about 90º.
Fracture Conchoidal to uneven
Tenacity Brittle
In Group Silicates; Tectosilicates; Feldspar Group
Striking Features Play of color, hardness, cleavage, and crystal forms
Environment In igneous environments in diabase, and in contact metamorphic rocks.
Rock Type Igneous, Metamorphic
Popularity (1-4) 2
Prevalence (1-3) 2
Demand (1-3) 1

Labradorite AUCTIONS

 -  Variety of Labradorite from Finland that displays a schiller color effect with intense colors such as dark red, orange, yellow, blue, and green.

Labradorite is a popular mineral, and it makes a unique gemstone. It is cut and polished into cabochons and beads, and occasionally as other facets. Some exquisite ornaments are carved out of large Labradorite chunks.

Perhaps the most colorful Labradorite comes from Finland at the Ylamaa Quarries, Lappeenranta. Two other outstanding localities are Golovinskoye, Zhytomyr, Ukraine; and the Antsohamamy Quarry, Tulear Province, Madagascar. Good Labradorite also comes from Black Hill, New South Wales, Australia.

Some of the most important Labradorite deposits are in Canada in Labrador, at Nain and Tabor Island. In the U.S., the Adirondack Mountains of upstate New York have produced colorful Labradorite, especially at Saranac Lake. Franklin Co.; Blue Ridge Road, North Hudson, Essex Co.; and Roaring Brook Falls, Keene Valley, Essex Co. A transparent form of Labradorite comes from Millard Co., Utah; and from the Woodward Ranch, near Alpine, Brewster Co., Texas.

Quartz, Muscovite, Biotite, Hornblende, Augite

Due to its unique color effect, Labradorite is easily distinguished from all minerals. However, specimens that don't exhibit labradorescence may be confused with many minerals, especially other feldspars.

labradorite PHOTOS
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