(mineralogy) Potassium aluminum silicate, KAlSi₃O₈, a common feldspar of igneous, plutonic, and metamorphic rocks. Orthoclase is the main feldspar of pegmatite occurrences, where it is most commonly flesh-colored. Orthoclase is used in the ceramic and glass industries and as a decorative gravel.

plural of orthoclase

(mineralogy) Of or relating to orthoclase.