Alkali Feldspars - (Na,K)(AlSi₃)O₈

Habit: Colorless, white, gray, pale yellow, pink or green. Crystals commonly short, prismatic and tabular; also cleavable,granular or massive. Vitreous luster, but pearly on cleavages;transparent to translucent. White streak.

Environment: The common feldspar of granites, granitepegmatites and syenites. Found in cavities in basalts, inhigh-grade metamorphic rocks and as a result of potassichydrothermal alteration.

Etymology: Orthoclase comes from the Greek orthos, meaning"right," and kalo, meaning "I cleave," in allusion to themineral’s right angle of good cleavage. Sanidine is fromthe Greek word for "tablet" or "board," a reference to itscommon habit. Anorthoclase derives from the Greek for"oblique" and "fracture," descriptive of the mineral’s cleavage.Microcline is from the Greek words for "little" and "inclined,"for its small deviation from monoclinic symmetry.

Used in ceramics and as a mild abrasive, microcline is thecommon feldspar mineral. Orthoclase is a major component of granite; its pink crystals give the rock its characteristic color.