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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
KAlSi
3
O
8
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
ALL ABOUT
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.
USES
Orthoclase is a rare gemstone and is faceted into gemstone cuts for jewelry such as pendants, earrings, and pins.
OTHER NAMES
Noble Orthoclose
Orthoclase
TREATMENTS AND ENHANCEMENTS
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.
SIMILAR GEMSTONES
Citrine
,
Heliodor
,
and
Topaz
are all softer.
Orthoclase
PHOTOS
[Click photos for more details]
Orthoclase
IN THE ROUGH PHOTOS
[Click photos for more details]
ADDITIONAL RESOURCES
The mineral Orthoclase
DISCUSSION
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