(mineralogy) 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.
Chemical composition: Potassium aluminum silicate, <math>KAlSi?_3O_8</math>
Physical properties: Moh's Hardness: 6.0 Specific gravity: 2.6 Color: white, flesh, yellow, brown, occasionally colorless Luster:
glassy Fracture: conchoidal Cleavage: two good at 90Âº
Habit: Monoclinic - prismatic. Well developed crystal faces are at 90Âº to each other. Occasional twinned crystals are found. Crystal faces typically look polished, and are not striated.