What is "brookite"

Brookite \Brook"ite\, n. [Named from the English mineralogist, H. J. Brooke.] (Min.) A mineral consisting of titanic oxide, and hence identical with rutile and octahedrite in composition, but crystallizing in the orthorhombic system.

n. (context mineral English) A dark brown mineral form of titanium dioxide, with the chemical formula titaniumoxygen₂.

Brookite is the orthorhombic variant of titanium dioxide, TiO, which occurs in four natural polymorphic forms (minerals with the same composition but different structure). The International Mineralogical Association (IMA) recognizes these four forms; the others are akaogiite ( monoclinic), anatase ( tetragonal) and rutile ( tetragonal). Brookite is rare compared to anatase and rutile and, like these forms, it exhibits photocatalytic activity. Brookite has a larger cell volume than either anatase or rutile, with 8 TiO groups per unit cell, compared with 4 for anatase and 2 for rutile. Iron Fe, tantalum Ta and niobium Nb are common impurities.

It was named in 1825 by French mineralogist Armand Lévy for Henry James Brooke (1771–1857), an English crystallographer, mineralogist and wool trader.

Arkansite is a variety of brookite from Arkansas, US, that is also found in the Murunskii Massif, in the Eastern Siberian region of Russia, where many other unusual minerals occur.

At temperatures above about 750 °C, brookite will revert to the rutile structure.