BROOKITE

Brookite is an orthorhombic form of titanium dioxide (TiO2) and is one of four recognized natural polymorphs, differing in structure while sharing the same composition. The other three polymorphs are akaogiite (monoclinic), anatase (tetragonal), and rutile (tetragonal). Compared to anatase and rutile, brookite is relatively rare and, like its counterparts, demonstrates photocatalytic properties. It features a larger cell volume, containing eight TiO2 units per cell, in contrast to anatase's four and rutile's two. Common impurities found in brookite include iron (Fe), tantalum (Ta), and niobium (Nb). 

The mineral was named in 1825 by French mineralogist Armand Lévy in honor of Henry James Brooke, an English crystallographer and mineralogist. A specific variety known as arkansite is found in Magnet Cove, Arkansas, and brookite is also located in the Murun Massif on the Olyokma-Chara Plateau in Eastern Siberia, Russia. At temperatures exceeding approximately 750 °C, brookite transforms back into the rutile structure.