Ilmenite

Ilmenite
Ilmenite from Miass, Ilmen Mts, Chelyabinsk Oblast', Southern Urals, Urals Region, Russia. 4.5 x 4.3 x 1.5 cm
General
Category	Oxide mineral
Formula (repeating unit)	iron titanium oxide, FeTiO 3
Strunz classification	4.CB.05
Dana classification	04.03.05.01
Crystal system	Trigonal
Crystal class	Rhombohedral (3) H-M symbol: (3)
Space group	R3
Unit cell	a = 5.08854(7) c = 14.0924(3) [Å]: Z = 6
Identification
Color	Iron-black; gray with a brownish tint in reflected light
Crystal habit	Granular to massive and lamellar exsolutions in hematite or magnetite
Twinning	{0001} simple, {1011} lamellar
Cleavage	absent; parting on {0001} and {1011}
Fracture	Conchoidal to subconchoidal
Tenacity	Brittle
Mohs scale hardness	5–6
Luster	Metallic to submetallic
Streak	Black
Diaphaneity	Opaque
Specific gravity	4.70–4.79
Optical properties	Uniaxial (–)
Birefringence	Strong; O = pinkish brown, E = dark brown (bireflectance)
Other characteristics	weakly magnetic
References

Ilmenite is the titanium-iron oxide mineral with the idealized formula FeTiO
3. It is a weakly magnetic black or steel-gray solid. From the commercial perspective, ilmenite is the most important ore of titanium. Ilmenite is the main source of titanium dioxide, which is used in paints, fabrics, plastics, paper, sunscreen, food and cosmetics.

Ilmenite crystallizes in the trigonal system. The ilmenite crystal structure consists of an ordered derivative of the corundum structure; in corundum all cations are identical but in ilmenite Fe²⁺ and Ti⁴⁺ ions occupy alternating layers perpendicular to the trigonal c axis. Containing high spin ferrous centers, ilmenite is paramagnetic.

Ilmenite is commonly recognized in altered igneous rocks by the presence of a white alteration product, the pseudo-mineral leucoxene. Often ilmenites are rimmed with leucoxene, which allows ilmenite to be distinguished from magnetite and other iron-titanium oxides. The example shown in the image at right is typical of leucoxene-rimmed ilmenite.

In reflected light it may be distinguished from magnetite by more pronounced reflection pleochroism and a brown-pink tinge.

Samples of ilmenite exhibit a weak response to a hand magnet.

Ilmenite most often contains appreciable quantities of magnesium and manganese and the full chemical formula can be expressed as (Fe,Mg,Mn,Ti)O₃. Ilmenite forms a solid solution with geikielite (MgTiO
3) and pyrophanite (MnTiO
3) which are magnesian and manganiferous end-members of the solid solution series.