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The Gemstone Orthoclase

Orthoclase as a mineral is a common feldspar, but when described as a gemstone it refers to a rare transparent yellowish form of the mineral Sanidine that is found in Madagascar. Until recently, this gemstone was though to be Orthoclase, and only recently have analyses determined it as being Sanidine. Despite this, it is still called Orthoclase on the gemstone market since the name has already been established. This gemstone can have a very pleasant yellow color, sometimes with some hints of brown in it. A purer yellow color is more desirable, although champagne colored stones are also popular. A new, apple-green type has recently been discovered, though its production is very limited.
Chemical Formula KAlSi3O8
Color Green, Yellow
Hardness 6 - 6.5
Crystal System Monoclinic
Refractive Index 1.52 - 1.53
SG 2.56 - 2.59
Transparency Transparent
Double Refraction -.008
Luster Vitreous
Cleavage 2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal
Mineral Class Sanidine

Orthoclase AUCTIONS

The color of Orthoclase gemstones is natural and is not enhanced by heat treatment. Occasionally the colorless, transparent forms from Switzerland are also cut as gemstones, but in general Orthoclase gemstones are yellow. Some Orthoclase gems display a cat's eye effect when cut into cabochon. Orthoclase may be fluorescent with a weak orange or bluish color.

Orthoclase is a rare gemstone and is faceted into gemstone cuts for jewelry such as pendants, earrings, and pins.


Orthoclase gemstones are not treated or enhanced.

Orthoclase SOURCES
Mostly from Madagascar, but also from Myanmar (Burma), Tanzania, and Brazil. The Madagascar locality provides the stones of the deepest color.

Citrine, Heliodor, and Topaz are all softer.

Orthoclase PHOTOS [Click photos for more details]

Orthoclase IN THE ROUGH PHOTOS [Click photos for more details]

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