An important feldspathoid mineral KAlSi2O6; sp. gr. 2.5; hardness 5.5–6.0; tetragonal; normally white or grey; vitreous lustre; crystals form very characteristic tetragonal trioctohedra; cleavage imperfect {110}; occurs in potassium-rich rocks which may be silica deficient, such as leucite-basanites, leucite tephrites, lamproites, and leucitophyres or leucitites.