A rare mineral tectosilicate found in volcanic rocks high in potassium and low in silica. Kaliophilite is one of three polymorphic forms of KAlSiO₄; the others are the rare mineral kalsilite and an orthorhombic phase formed artificially at about 930°F (500°C). It crystallizes in the hexagonal system in prismatic crystals with poor prismatic and basal cleavage. The hardness is 6 on Mohs scale, and the specific gravity is 2.61. At high temperatures a complete solid-solution series exists between KAlSiO₄ and NaAlSiO₄, but at low temperatures the series is incomplete. The principal occurrence of kaliophilite is at Monte Somma, Italy.