Orthoclase

Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite. Typically, the pure potassium endmember of orthoclase forms a solid solution with albite, the sodium endmember (NaAlSi3O8), of plagioclase. While slowly cooling within the earth, sodium-rich albite lamellae form by exsolution, enriching the remaining orthoclase with potassium. The resulting intergrowth of the two feldspars is called perthite. The higher-temperature polymorph of KAlSi3O8 is sanidine. Sanidine is common in rapidly cooled volcanic rocks such as obsidian and felsic pyroclastic rocks, and is notably found in trachytes of the Drachenfels, Germany. The lower-temperature polymorph of KAlSi3O8 is microcline. Adularia is a low temperature form of either microcline or orthoclase originally reported from the low temperature hydrothermal deposits in the Adula Alps of Switzerland. It was first described by Ermenegildo Pini in 1781. The optical effect of adularescence in moonstone is typically due to adularia. The largest documented single crystal of orthoclase was found in the Ural mountains in Russia. It measured ~10×10×0.4 m and weighed ~100 tons.

Orthoclase is commonly used as a raw material for manufacturing certain types of glass and porcelain. It is also a constituent of scouring powder. The intergrowths of orthoclase are called Moonstones when used in jewelry making and are known for their attractive sheen (adularescence).

Orthoclase is the official state gem of Florida (USA).

Orthoclase is an excellent stone for believers who need emotional healing and the restoration of hope and enthusiasm for life. It can be used to align all of the chakras, but is mainly linked to the Solar Plexus chakra. It aims to restore vitality and is often used to enhance exercise and encourage proper breathing patterns.