Isolated, rare mineral of the clinopyroxenes with the composition NaAlSi2O6; sp. gr. 3.2–3.4; hardness 6; granular crystals or massive; jade is the precious variety of jadeite, although the term includes the amphibole mineral nephrite; it occurs with albite in blueschists (glaucophane schists) under conditions of low temperature and high pressure at destructive plate margins.