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	6Â -Â 6.5
Crystal System	Monoclinic
Refractive Index	1.52Â -Â 1.53
SG	2.56Â -Â 2.59
Transparency	Transparent
Double Refraction	-.008
Luster	Vitreous
Cleavage	2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal
Mineral Class	Sanidine