Brookite is a mineral with the chemical formula TiO₂. It belongs to the oxide group, crystallizes in the orthorhombic system, has a hardness of 5.5–6 on the Mohs scale, a subconchoidal fracture, weak cleavage, an adamantine luster, and a white, gray, or yellowish streak. It is one of the three mineral forms of titanium dioxide, along with anatase and rutile.