Titanium dioxide, occurs in nature as the well-known minerals rutile, anatase and brookite. It is additionally for its two high pressure forms, a monoclinic baddeleyite-like form and an orthorhombic α-PbO2-like form, both recently found at the Ries crater in Bavaria. It is mainly sourced from ilmenite ore. This is the most widespread form of titanium dioxide-bearing ore in the world. Rutile is the next most abundant and contains around 98% titanium dioxide. The metastable anatase and brookite phases convert irreversibly to the equilibrium rutile phase when heated above temperatures in the 600–800 °C (1,112–1,472 °F) range.