A minor accessory mineral, formula CaTiO₃, occurring in basic rocks. Perovskite has given its name to a large family of materials, synthetic and natural, crystallising in similar structures. The crystal structure is ideally cubic, with a framework of corner-sharing octahedra, containing titanium (Ti) or other relatively small cations surrounded by six oxygen (O) or fluorine (F) anions (see illus.). Within this framework are placed calcium (Ca) or other large cations, surrounded by twelve anions. Tilting of the octahedra and other distortions often lower the symmetry from cubic, giving the materials important ferroelectric properties and decreasing the coordination of the central cation. This flexibility gives the structure the ability to incorporate ions of different sizes and charges. Substitution of niobium (Nb), cerium (Ce), and other rare-earth elements in natural calcium titanate (CaTiO₃) is common and can make perovskite an ore for these elements.