NaAlSi2O6

NaAlSi2O6 is a sodium aluminum silicate that serves as the end-member composition of the jadeite group within the pyroxene family. In mineralogical terms, it is a clinopyroxene with the general XY(Si,Al)2O6 formula, where X is Na and Y is Al. The structure consists of single chains of corner-sharing SiO4 tetrahedra, with Al substituting for Si in the tetrahedral sites and Na occupying a nearby octahedral site to balance charge. Jadeite crystallizes in the monoclinic system and typically forms prismatic to blocky crystals.

Occurrence and formation theories indicate that jadeite forms under high-pressure, subduction-zone metamorphic conditions. It is commonly associated with blueschists and eclogites and can occur in ultramafic and metasedimentary rocks altered under extreme pressure. Gem-quality jadeite, particularly rich green varieties, are sourced from several well-known localities, including parts of Myanmar, Guatemala, and Japan.

Physical properties of jadeite include a hardness around 6.5 to 7 on the Mohs scale and a specific gravity in the range of about 3.2 to 3.5. The mineral typically presents a vitreous luster and can range in color from white to vivid emerald-green, with green coloration often enhanced by trace chromium and other elements. Jadeite is translucent to opaque, with crystals that are frequently used as gemstones when coloration and clarity are suitable.

Uses and cultural relevance center on its role as a gemstone, widely known as jadeite jade when cut and polished for jewelry and carvings. It should be distinguished from nephrite, the other jade variety, which has a different chemical composition and mineral structure.