Brookite is the orthorhombic variant of titanium dioxide (TiO2), which occurs in four known natural polymorphic forms (minerals with the same composition but different structure).

Brookite is rare compared to anatase and rutile and, like these forms, it exhibits photocatalytic activity.

[6] Iron (Fe), tantalum (Ta) and niobium (Nb) are common impurities in brookite.

It is also found in the Murun Massif on the Olyokma-Chara Plateau of Eastern Siberia, Russia, part of the Aldan Shield.

Beautiful, deep red crystals (seen above-right) similar to pyrope and almandite garnet are also known.

[3][4] Associated minerals include its polymorphs anatase and rutile, and also titanite, orthoclase, quartz, hematite, calcite, chlorite and muscovite.

[4] The type locality is Twll Maen Grisial, Fron Olau, Prenteg, Gwynedd, Wales.