The principal titanium minerals are rutile (titanium oxide) and ilmenite (iron titanate).
rutile and ilmenite both have high specific gravity and are little affected by weathering.
Biotite, if present, is brown; epidote is yellow or colourless; rutile, apatite and quartz all occur with some frequency.
There is no distinct cleavage (rutile and anatase have cleavages); hardness 5-6; sp.
Minute crystals of brookite have been detected with anatase and rutile in the iron-ore of Cleveland in Yorkshire.
Brookite occurs only as crystals, never in compact masses, and is usually associated with either anatase or rutile.
rutile is much lighter, 4·2, and the streak light-brown; tourmaline is only 3·2.
Its most common ore is rutile (TiO2), which resembles silica in many respects.
Titanic acid occurs in nature crystallized in anatase, arkansite, brookite, and rutile.