ALBITE, a mineral of the felspar group and forming the sodic end member of the plagioclases (q.v.) (from the Lat. albus, in allusion to the white colour of its crystals). Albite crystallizes in the triclinic system and has the chemical composition In petrology the name is not restricted to the pure sodium compound but is arbitrarily adopted for mixtures con taining up to Io% of the anorthite molecule, with which it forms solid solutions. Albite forms an essential con stituent of many acid and alkaline igneous rocks, in granite, syenite, porphyry, trachyte, etc., whilst in the crystalline schists it is not infrequent as a metamorphic mineral.