A mineral oxide CaTiO₃; sp. gr. 3.98–4.26; hardness 5.5; monoclinic or orthorhombic; tiny, cubic crystals; yellow-brown to black; common accessory mineral in undersaturated (see silica saturation) alkaline igneous rocks found with nepheline or melilite. Occasionally occurs in some ultramafic (see ultrabasic), plutonic, igneous rocks.