"Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Three rarer polymorphs of TiO2 are known:Anatase (sometimes known by the obsolete name \"octahedrite\"), a tetragonal mineral of pseudo-octahedral habitBrookite, an orthorhombic mineralTiO2 (B), a monoclinic form.Rutile has among the highest refractive indices at visible wavelengths of any known crystal, and also exhibits a particularly large birefringence and high dispersion."@en . "Rutile"@en . . .