ILMENITE or TITANIC IRON-ORE, an min eral resembling haematite in form and habit and formerly re garded as a titaniferous haematite It is now considered to be an iron titanate, isomorphous with pyrophanite (MnTiO3) and geikielite, The composition indicated by the formula is Fe0 = 4 7.4 and TiO2= 5 2.6 % ; but analyses show wide variations due to the presence of an excess of ferric oxide and, in some varieties, magnesia. Ilmenite crystallizes in the hexagonal system with rhombohedral symmetry. Well-formed crystals are rare. The mineral is distinguished from haematite by its black streak and slight magnetism. It is, however, not polar, like mag netite. Hardness, 5. Sp. G., 4.8. Colour, black. Lustre, sub metallic. Opaque. The name is derived from the Ilmen moun tains in the southern Urals.
Ilmenite occurs in association with magnetite in gneisses and schists, often in beds of considerable size, but of little economic value. It is a frequent constituent of the more basic igneous rocks, as magnetite is of the more acid types. Some of the black sands derived from these rocks consist largely of grains of ilmenite. For titano-magnetite see under MAGNETITE. (F. H. HA.)