Feldspar

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Chemical composition -- A family of complex aluminosilicates that are the most common minerals in the Earth's crust.

Color -- a wide range of colors.

Optics -- R.I. 1.52-1.54.

Durability -- Hardness 6-6.5.

Crystal structure -- Monoclinic or triclinic, depending on composition.

Specific Gravity -- 2.54-2.63.

Sources -- Many widely scattered locales, depending on composition.

Varieties --


Moonstone

A colorless to yellowish gray, highly translucent to semitransparent variety of feldspar that reflects light in a distinctive shimmering phenomenon known as adularescence. Sometimes, moonstone cabochons display a well-defined cat's-eye effect (a bright line caused by reflection from tiny parallel inclusions). The most prized moonstones are colorless and nearly transparent with a blue sheen effect; Sri Lanka (Ceylon) is the primary source. India is another major source.

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Orthoclase

A transparent yellow feldspar resembling citrine quartz or yellow beryl, found primarily in Madagascar and used primarily in collections.

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Amazonite

An opaque light green to blue-green feldspar with a distinctive mottled or striated appearance that is often cut en cabochon.

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Labradorite

A gray or colorless to yellow feldspar containing inclusions of other materials that produce a variety of visual effects. A diffuse cloud of small platelike inclusions produces a distinctive, shimmering effect known as schiller. Oregon produces semitransparent to transparent red to green (or bicolored) material ( sunstone , heliolite , or plushstone ). Brilliantly iridescent blue/purple/yellow/green material from Finland is known as spectrolite .
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