description Orthoclase Overview
Orthoclase is a potassium-rich tectosilicate feldspar with the ideal formula KAlSi3O8 and a monoclinic crystal structure. It is a common rock-forming mineral in igneous rocks and also occurs in some metamorphic and sedimentary settings. Transparent yellow to champagne orthoclase may be faceted as a gemstone, while microscopic intergrowths of orthoclase and albite produce the adularescence seen in the feldspar gem variety moonstone.
help Orthoclase FAQ
What is orthoclase made of?
Orthoclase is a potassium-rich feldspar with the ideal formula KAlSi3O8. It has a monoclinic crystal structure and is a common rock-forming mineral.
What color is gem-quality orthoclase?
Transparent orthoclase is often yellow, golden, or champagne colored. The clearest material may be faceted, while opaque or heavily included specimens are more often collected as minerals.
Where is orthoclase found?
Orthoclase forms in many igneous rocks, especially potassium-rich rocks such as granite. It also occurs in some metamorphic and sedimentary settings.
How is orthoclase different from moonstone?
Moonstone is a feldspar gemstone whose visible sheen comes from light scattering between feldspar layers. Orthoclase can be one of the feldspars involved, but ordinary transparent orthoclase does not automatically show moonstone adularescence.
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