Mineral, FeTiO₃; sp. gr. 4.5–5.0; hardness 5–6; trigonal; black; black to brownish-red streak; sub-metallic lustre; crystals normally thick and tabular, but often massive and compact; no cleavage; magnetic; occurs as an accessory mineral in igneous rocks, e.g. gabbro and diorite, in quartz veins and pegmatites, in gneisses, in association with hematite and chalcopyrite, and because it is resistant to weathering it occurs extensively in alluvial deposits with magnetite, monazite, and rutile. It is used as a source of iron and titanium. The name is derived from that of the Ilmen Mountains, Russia.