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Labradorite (Feldspar Family)

Labradorite (Feldspar Family)

The iridescent property of laboradite, as shown here, results from light diffracting off closely spaced layers of calcium and sodium-rich feldspar. As the stone is turned, flashes of blue, green, yellow, and red are visible across properly oriented surfaces. The highest quality laboradite is generally cut as cabochons or used for carvings, as seen here. The most important sources of laboradite are Laborador (for which the mineral is named), Finland, and Madagascar.

Labradorite (Feldspar Family)

Labradorite (Feldspar Family)

The minerals in the feldspar family make up more than half of the Earth's crust. Occasionally these common minerals form crystals that shimmer like the light of the moon or a rainbow on a soap bubble. Called iridescence, this phenomenon is caused by light scattering, or diffracting, off closely spaced layers in the feldspar crystals. The gems cut from these iridescent crystals are called moonstones, sunstones, and labradorite. Sunstones exhibit a reddish to golden schiller, resulting from light reflecting off numerous tiny copper or hematite (iron oxide) flakes scattered within the stones. Varying amounts of copper in Oregon sunstone cause the gems to range in color from colorless to yellow, as well as shades of green, red and pink. Some gems contain several colors, as seen in the carved sunstones pictured here. The pendant at far left was designed and carved by Nancy Chan and Greg Fraser; the center hexagonal-shaped sunstone, "Spitfire," is 4.53 carats and was faceted by Paul Paulson; the sunstone at far right, "Eternal Flight," is 174 carats and was carved by Bobbie Lorett. This suite of carved and faceted Oregon Sunstones was a wonderful addition to the National Gem Collection in 2004.

Orthoclase (Feldspar Family)

Orthoclase (Feldspar Family)

The name orthoclase is from the Greek for "straight fracture," because its two cleavage planes are at right angles to each other. Orthoclase belongs to the feldspar family of minerals that make up more than half of the Earth's rocky crust. Occasionally these common minerals form crystals that are gem quality. Orthoclase can be found as a transparent colorless, champagne, or yellow gem resembling citrine quartz or yellow beryl. This 250-carat gem is unusual because orthoclase rarely occurs in a colorful transparent form. It is rare because of its size, transparency, and vibrant yellow color. This orthoclase is from Madagascar, the most important source for gem-quality orthoclase.

Orthoclase Feldspar (variety: Moonstone)

Orthoclase Feldspar (variety: Moonstone)

The minerals in the feldspar family make up more than half of the Earth's rocky crust. Occasionally these common minerals form crystals that shimmer like the light of the moon or a rainbow on a soap bubble. Called iridescence, this phenomenon is caused by light scattering, or diffracting, off closely spaced layers of different composition in the feldspar crystals. The gems cut from these iridescent crystals are called moonstone, sunstone, and labradorite. This 35.38 carat moonstone is from Tanzania. Moonstones are prized for their beautiful blue iridescence, known as adularescence. Flawless, clear, or translucent gems exhibiting a rich blue sheen are most valuable. Moonstones are typically cut as cabochons to best show off the effect. The finest moonstone gems come from Sri Lanka, Burma, and India. This is the first moonstone from Tanzania for the National Gem Collection.

Sunstone

Sunstone

The minerals in the feldspar family make up more than half of the Earth's crust. Occasionally these common minerals form crystals that shimmer like the light of the moon or a rainbow on a soap bubble. Called iridescence, this phenomenon is caused by light scattering, or diffracting, off closely spaced layers in the feldspar crystals. The gems cut from these iridescent crystals are called moonstones, sunstones, and labradorite. Sunstones exhibit a reddish to golden schiller, resulting from light reflecting off numerous tiny copper or hematite (iron oxide) flakes scattered within the stones. The golden sheen flashing off of this sunstone from Norway is due to the hematite inclusions.


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