Brookite: Gemstone Information
One of the polymorphs of titanium dioxide (TiO2), with rutile and anatase, brookite, which crystallizes in the orthorhombic system with varied habit, has been used ornamentally. It is yellowish brown to reddish brown with hardness of 5.5–6. The SG varies from 3.87 to 4.08 and the RIs are near to 2.583 and 2.705 for the principal rays; the biaxial and optically positive DR is about 0.122, but it can reach 0.157 in certain cases. The lustre of brookite is metallic adamantine. Examples are found in France, Switzerland, Russia (Urals) and the USA.