Labradorite is a plagioclase feldspar famous for its labradorescence: broad flashes of blue, green, gold, orange and sometimes purple that appear when the stone is turned under light. The colors come from light interfering within extremely thin internal layers, not from pigments. Labradorite was named for the Labrador coast of Canada, where Europeans first described it in the 1770s. Finland produces an especially colorful type sold as spectrolite, and transparent labradorite from India and Madagascar is sold as "rainbow moonstone."
What labradorite is
Feldspars are the most common minerals in the Earth's crust. They fall into two groups: the potassium feldspars (such as orthoclase and microcline) and the plagioclase feldspars, a series that runs from sodium-rich albite to calcium-rich anorthite. Labradorite sits toward the calcium-rich end of that series.
Labradorite is common in igneous rocks such as gabbro, basalt and anorthosite. Most of it is gray and shows no special effect. Gem labradorite, with strong labradorescence, comes from rocks that cooled slowly enough for internal layering to develop. The page on igneous rocks and gemstones covers these rocks.
Other feldspar gems are close relatives. Moonstone is usually orthoclase or albite with a soft blue-white glow. Sunstone is a feldspar with glittering metallic inclusions.
How labradorescence works
As some plagioclase cools, it separates into extremely thin alternating layers of two slightly different compositions. These layers, called lamellae, are close in thickness to the wavelengths of visible light. When light enters the stone, some of it reflects off each layer boundary. Reflected light waves from different layers interfere with each other. Some wavelengths reinforce, producing strong color, while others cancel out.
The color you see depends on the thickness of the layers and the angle of viewing. Thinner layers give blue and violet; thicker ones give yellow, orange and red. Because the layers can change thickness across a stone, one piece can show several colors in patches.
This is the same physics that makes colors on soap bubbles and oil films. The effect is directional: the stone may look dull gray from one angle and then flash brightly as you tilt it. Our page on gemstone optics compares labradorescence with adularescence in moonstone, aventurescence in sunstone and play-of-color in opal.
Sources and history
Labrador, Canada
Labradorite was described from the Labrador coast, in what is now Newfoundland and Labrador, Canada. Moravian missionaries working on the coast collected samples in the 1770s, and the stone became fashionable in Europe in the late 18th and 19th centuries. The Inuit and other peoples of the region knew the stone long before that. A traditional Inuit story says the northern lights were trapped in the rocks along the coast and that a warrior freed most of them with a blow of his spear, leaving some lights still caught in the stone.
Spectrolite from Finland
During World War II, labradorite with very strong, full-spectrum colors was found in southeastern Finland near Ylämaa. Finnish geologist Aarne Laitakari is credited with the name spectrolite, which refers to the stone's display of the full spectrum. Spectrolite usually has a dark, nearly black background that makes its colors stand out. The name is often applied to any labradorite with strong color on a dark body, though strictly it refers to the Finnish material.
Madagascar and other sources
Madagascar has become a large source of labradorite with strong blue and gold flashes, often cut into large cabochons, carvings and polished pieces. The page on the gems of Madagascar covers the island's other gems. Labradorite also comes from India, Russia, Norway, Mexico and the United States.
Transparent labradorite with yellow, orange or red color and no labradorescence comes from Oregon, Mexico and elsewhere. Some of these stones overlap with sunstone in trade names.
Rainbow moonstone
"Rainbow moonstone" is a trade name for colorless to white transparent labradorite with a blue or multicolored sheen. It comes mainly from India and Madagascar. Despite the name, it is a plagioclase feldspar, not the orthoclase or albite usually called moonstone. Many gemologists prefer the term "rainbow labradorite" or "white labradorite." The trade name is widely used, so buyers should know what it means.
Rainbow moonstone often contains small black inclusions or needles, which help separate it from glass imitations.
Cutting labradorite
Labradorescence only shows clearly from certain directions. The cutter must orient the stone so the layers lie parallel to the base of the cabochon, so the colors flash toward the viewer face up. A poorly oriented stone may look gray from the front and show color only from the side.
Labradorite is usually cut as cabochons, free-form pieces, beads and carvings. Transparent material is sometimes faceted. Large polished slabs and spheres show off the effect for decorative use.
Durability and care
Labradorite is about 6 to 6.5 on the Mohs scale, slightly softer than quartz. It has two directions of cleavage, one perfect, so it can split or chip if struck. Many stones also contain internal cleavage cracks that show as flat, shiny planes.
Labradorite works well in pendants and earrings. In rings and bracelets, choose a protective setting such as a bezel and avoid knocking the stone. The page on cleavage in gemstones explains the risk, and gemstone durability compares feldspars with other jewelry gems.
Clean labradorite with warm soapy water and a soft cloth. Avoid ultrasonic and steam cleaners, harsh chemicals and sudden temperature changes.
Buying labradorite
The strength, range and coverage of the color matter most. Strong blue labradorite is common. Stones that show several colors, especially gold, orange, red and purple, are rarer. Full coverage across the face of the stone is better than small patches. Dark body color makes the flashes stand out. Cracks and cleavage planes that reach the surface lower value and durability.
Glass and coated imitations exist, but natural labradorite's color changes sharply with angle and usually shows internal cleavage, needles or dark inclusions.
Frequently asked questions
What causes the colors in labradorite?
Very thin internal layers of slightly different feldspar compositions reflect light, and the reflected waves interfere to create color. The colors change with viewing angle.
Is rainbow moonstone a real moonstone?
Rainbow moonstone is a trade name for transparent labradorite with a colorful sheen. It is a plagioclase feldspar, not the orthoclase or albite usually called moonstone.
What is spectrolite?
Spectrolite is a name for labradorite from Finland with intense, full-spectrum colors on a dark background. The name is sometimes used for similar material from elsewhere.
Is labradorite good for everyday rings?
It is moderately hard but has perfect cleavage, so it can chip or split from a knock. A protective setting and careful wear help.