Mineral, Na(AlSi2O6) H2O; sp. gr. 2.2–2.3; hardness 5.0–5.5; cubic; can be colourless or white, with grey, red, and greenish tints, sometimes pigmented with iron oxides; vitreous lustre; crystals polyhedra and tetragonal trioctahedra, also found in granular aggregates; cleavage poor, cubic; occurs in rocks of low-temperature igneous origin that are rich in soda and water (e.g. nepheline syenites), and also volcanic tuffs.
Subjects: Earth Sciences and Geography.