An accessory mineral, TiO2; iron, niobium, and tantalum may also be present; sp. gr. 4.2–5.6; hardness 6.0–6.5; tetragonal; normally reddish-brown, but also yellowish-red, or black; pale brown streak; adamantine lustre; crystals normally square prisms terminated by pyramids; cleavage prismatic {110} and {100}; occurs in a variety of igneous rocks, schists, gneisses, and metamorphic limestones and quartzites, and becomes concentrated in alluvial deposits and beach sands. It is an important ore mineral for titanium and its compounds.