Rutile is a red-to-black oxide consisting of impure titanium (IV) oxide (TiO₂), a titanium ore of widespread occurrence, found in igneous and metamorphic rocks and quartz veins. Rutile occurs as long prismatic and needle-like crystals in the tetragonal system and as granular masses. It has a metallic luster and is britlle. It is used to color porcelain and as a gemstone. Hardness 6–6.5; relative density 4.2.