Orthoclase

A orthoclase (of the Greek orthos : “right”) is a Minéral of the family of the potassic feldspars. Its chemical composition is.

Properties

Orthoclase is named thus following its faculty to cleave according to two orthogonal plans. It crystallizes in a monoclinical system.

Orthoclase has a Dureté of 6, and is used as reference on the scale of hardness Mohs. Its Densité lies between 2,56 and 2,58. The macle of Carlsbad is frequent.

Layer

Orthoclase is present in the plutonic rocks and metamorphic and is only seldom in the Lave S.

Varieties

The moon stone is an opalescent variety of orthoclase which evokes the clearness of the moon. The cause is the reflection of the light by the internal structure, formed of plates of Albite and orthoclase. If the layers are sufficiently fine, they give a pretty blue, if not the Adularescence, white, is less appraisal. A reflection in only one band can give a moon stone cat's eye. The large stones of good quality are rare and expensive. The moon stone is rather sensitive to the shocks. It comes from Sri Lanka (transparent with blue reflections), from Burma (most beautiful), but also from Australia, the United States of America, of India (gray, pink, white milky), of Madagascar, of Tanzania and even of the Alps.

Yellow orthoclase is a particular variety of orthoclase of color champagne. Being fragile, one cuts it in Taille emerald for the collectors. It comes from Madagascar and High Burma.

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