Ilmenite

Ilmenite is an iron titanium oxide and the most important commercial source of titanium. It crystallizes in the trigonal (hexagonal) system, usually appearing as thick tabular crystals, embedded grains, or massive aggregates with an iron-black to brownish-black color and a metallic to submetallic luster.

It is dense and opaque, and some specimens are weakly magnetic, especially where intergrown with magnetite or hematite. Its black streak and great weight distinguish it from many other dark minerals.

First recognized in Cornwall (as "menaccanite") and named for the Ilmen Mountains of Russia, ilmenite is now mined chiefly from titanium-rich beach sands around the world.

Ilmenite is a common accessory mineral in mafic and ultramafic igneous rocks such as gabbro, norite, and anorthosite, where it crystallizes from titanium- and iron-rich magmas, sometimes forming massive segregations of economic size.

It also occurs in some metamorphic rocks and pegmatites. Because it is hard and chemically resistant, ilmenite weathers out of these rocks and concentrates with magnetite, rutile, zircon, and monazite in heavy-mineral beach and stream placers — the dominant ore source today. Major deposits include Allard Lake in Quebec, the Tellnes deposit in Norway, and vast coastal sand operations in Australia, India, South Africa, and Mozambique.

Ilmenite is iron-black to brownish-black, opaque, with a metallic to submetallic luster, hardness 5-6, and a high density. Its streak is black to brownish-red, which helps separate it from hematite (cherry-red streak) and magnetite (black streak but strongly magnetic).

Ilmenite is generally only weakly magnetic on its own. Thick tabular crystals or rounded black grains in heavy sands, often with magnetite and zircon, are typical. Distinguishing it from magnetite in the field usually relies on its weaker magnetism; a streak test and magnet are the simplest checks against look-alike oxides.

Ilmenite is the leading ore of titanium, processed mainly to produce titanium dioxide pigment — the bright white colorant in paints, plastics, paper, inks, and sunscreens — and to make titanium metal sponge for strong, lightweight alloys.

It also yields titanium tetrachloride and other titanium chemicals, and is used as a heavy aggregate and in some welding and abrasive applications. Lunar soils are notably rich in ilmenite, making it a candidate resource for extracting oxygen and metals in future space exploration. It has no jewelry use.