The black iron titanium oxide mineral ilmenite (FeTiO3) is the primary ore for titanium, a metal needed to make a variety of high-performance alloys. It is also a common accessory mineral in igneous rocks, sediments, and the lunar regolith. Ilmenite crystals are found in a wide range of sizes and shapes. They are opaque, black to brownish-black and have a submetallic to metallic luster. It is a weakly magnetic mineral, and often shows intergrowth with hematite and magnetite in magmas and igneous and metamorphic rocks. Ilmenite typically forms as thick tabular crystals or anhedral masses embedded in igneous and metamorphic rocks, and as sand-sized grains in sedimentary rock deposits. It can also occur as black striations in gabbro, norite, or anorthosite.
The formation of ilmenite depends on the cooling conditions and rate of magma evolution. During the early stages of magma evolution, the minerals that form first are those with the lowest melting points and thus cool more rapidly than other magma components. As the magma continues to cool, these early-forming minerals segregate from the rest of the magma in a process called magmatic segregation. These magma components with low melting points, such as ilmenite and magnetite, concentrate at the bottom of the magma chamber. Ilmenite is formed in this manner and can be found as veins or sulfide-rich inclusions in gabbro, norite, and anorthosite, and in pegmatites.
Ilmenite is a naturally occurring mineral with a high specific heat and low viscosity. This mineral has a number of other useful properties that make it an important raw material for many industries. For example, ilmenite can be used as an ingredient in ceramic glazes to produce dark brown specks that are difficult to achieve with rutile. It is also used in combination with rutile to develop characteristic rutile break glazes and seeds crystals in titania glazes. It has a very low shrinkage when fired to high temperatures and is a good source of TiO2 (titanium dioxide).
A substantial percentage of the ilmenite mined in the world is used to manufacture titanium dioxide, an essential pigment, whiting and polishing abrasive. It is the primary source of titanium, which is needed to produce a variety of high-performance alloys, including aircraft engines, naval ships and tanks, and surgical instruments. The other main use for ilmenite is as a flux in steel production. Raw ilmenite is combined with carbon (anthracite) and energy in large electric arc smelters to convert it to molten iron and a slag rich in titanium. This slag is further processed to produce Pig Iron, continuous cast steel billets, and iron or steel powders for use in the manufacture of machinery and die castings. Ilmenite is shipped in bulk and is often kept as dry as possible to prevent deterioration while being transported. It is commonly stored in large covered stockpiles near ports.
