A framework structure silicate of the feldspathoidal mineral group. It is commonly found as euhedral phenocrysts in K₂O-rich and SiO₂-poor volcanic rocks, consistent with its chemical composition, (K,Na)AlSi₂O₆, where K is more abundant than Na. The crystals are typically white, and the luster varies from dull to vitreous. Mohs hardness lies between 5.5 and 6. Density ranges from 2.45 to 2.5. Crystals, exhibiting the characteristic isometric trapezohedral form (see illus.), as large as 7 cm (3 in.) are common in the lavas of Nyiragongo volcano, Zaire. Other well-known areas include West Kimberley, Australia; Mount Vesuvius, Italy; Highwood Mountains and Bearpaw Mountains, Montana; and the Leucite Hills, Wyoming.