A nesosilicate CaTiSiO4 (O,OH,F); sp. gr. 3.45–3.55; hardness 5; crystals wedge-shaped, occasionally massive; brown, grey, reddish brown, yellow, or black; monoclinic; adamantine to resinous lustre; occurs as a primary accessory mineral in calc-alkaline igneous rocks and alkaline igneous rocks in which it may occur as a major constituent along with apatite, nepheline, and aegirine. It is common in contact metamorphosed limestones, particularly skarns.