Ilmenite is usually weakly magnetic. I said usually because ilmenite itself is not magnetic but it is often intergrown with magnetite which very strongly responds to the magnetic force. Hence we can use a hand magnet (every mineral identifier should have one) and watch through the microscope (because ilmenite grains are typically very small) how the grains suspected to be ilmenite are behaving. If they are only lazily turning themselves but not jumping vigorously towards the magnet then they are most likely ilmenite grains.
Ilmenite crystal should ideally look like this.
Another aspect that separates ilmenite from magnetite is crystal structure. Magnetite is an isometric mineral, it forms double pyramids (octahedrons) just like diamond. These octahedrons are often worn off in sand but in this case magnetite is rounded and still roughly isometric. Ilmenite is at least theoretically different. Ilmenite grains tend to be tabular. However, in reality many ilmenite grains are still pretty equant. Ilmenite and magnetite are opaque minerals.
The crystal structure of ilmenite is identical to hematite. It is compositionally pretty close to hematite as well. The only difference between hematite and ilmenite is that one Fe atom (in hematite) is replaced by titanium atom (in ilmenite). The chemical formula of ilmenite is FeTiO3. This is ideal formula which often is pretty close to the reality but some of iron may be replaced with magnesium and manganese.
Beach sand from India containing lots of ilmenite. Most of the black grains are ilmenite crystals. Brown grain in the lower left is leucoxene. Light blue elongated grain is kyanite. Transparent crystals are quartz grains. The width of the view is 5 mm.
Ilmenite grains are often altered to leucoxene. Leucoxene is a mixture of several oxide minerals, it isn’t a mineral itself. It looks like a very fine-grained light-colored or brownish coating on ilmenite grains.
Ilmenite is found in igneous and metamorphic rocks although it very rarely forms a major component of a rock. If that happens (in iron and titanium rich magmatic cumulates) then it is usually mined for its titanium content. Titanium extracted from ilmenite in the form of titanium dioxide is used as a white pigment in paints and sunscreens among other things. Millions of tonnes of ilmenite are mined every year but the majority of it comes from sand, not from the hard rocks. Ilmenite is resistant to weathering and therefore common in sand. It is usually accompanied by magnetite and possibly by a small amount of rutile and zircon as well (they are even more resistant to weathering).
Tellnes mine in Norway. It is fun to think that white paint and sunscreen come from this black hole. Image: Mikenorton/Wikipedia.
