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Orthoclase is one of the most common minerals, and occurs in numerous mineral environments. It is polymorphous with Microcline and Sanidine. These three minerals form the Potassium Feldspar group. They are almost identical in physical properties, and it is sometimes impossible to distinguish one another without x-ray analysis. The only difference between them is their crystal structure. Microcline crystallizes in the triclinic system, and Orthoclase and Sanidine crystallize in the monoclinic system. Sanidine forms at high temperatures and has a disordered monoclinic symmetry, whereas Orthoclase forms at low temperatures and cools slowly, forming more ordered monoclinic crystals.
[For more information on the crystal structure of the feldspars, see "All about" in the mineral Anorthite.]

In many reference guides, Microcline and Sanidine are wrongly categorized as variety of Orthoclase. Since it is so difficult to distinguish between Orthoclase, Sanidine, and Microcline, they may be simply called "Potassium Feldspar".

Moonstone is a form of Adularia (or several other feldspars) that displays adularescence, exhibiting a color sheen on its surface. This phenomenon gives Moonstone important status and recognition on the gem market.

Help Uses Orthoclase is industrially important in the manufacture of glass and ceramics. Crystals and twins are studied by scientists, as they provide information on the formation of minerals and environmental factors. Well shaped crystals and twins are highly sought after by mineral collectors, and the variety Moonstone is an important gem. A transparent yellow variety from Madagascar is faceted as a gem for collectors

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Orthoclase is one of the most common minerals, and is found worldwide. Only a select few localities are mentioned:
Transparent yellow crystals have come from a pegmatite in Madagascar, and a similar material is found in the gem gravels of Myanmar (Burma). Much Adularia is found in the Alps in Switzerland, especially at Adular, the locality this variety was named after. "Carlsbad" twins are famous from Carlsbad, Czechoslovakia, and fine "Baveno" twins have come from Baveno, Italy. Large, well-formed crystals were found in Disentis, Switzerland. Light blue crystals occur in the Lake Baikal area in Russia,

In the U.S., enormous crystals were found on Sandia Mountain, Bernalillo Co, New Mexico. Famous collector specimens have come from Robinson, Colorado, and Goodsprings, Clark Co., Nevada. Orthoclase has also come from the French Creek mine, St. Peters, Chester Co., Pennsylvania. Much Adularia Moonstone has come from New Mexico.

Orthoclase Feldspar areas found in Tanzania.

large masses occur on Mt. Kilimanjaro, Tanzania, same, babati.