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:

Rutile has among the highest refractive indices at visible wavelengths of any known crystal, and also exhibits a particularly large birefringence and high dispersion. Owing to these properties, it is useful for the manufacture of certain optical elements, especially polarization optics, for longer visible and infrared wavelengths up to about 4.5μm.