crystals of brookite, crystals of quartz : Kharan, Balochistan (Baluchistan), Pakistan — Photo: Parent Géry · CC BY-SA 3.0
Brookite
The orthorhombic polymorph of titanium dioxide — alongside anatase, rutile and akaogiite.
Intro adapted from Wikipedia (CC BY-SA).
Brookite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula TiO₂.
It crystallizes in the orthorhombic crystal system (space group Pbca). It is a member of the Brookite structural group.
Key properties: Mohs hardness 5.5–6; specific gravity 4.08–4.18; typically brown or black or red; White to grayish white or yellowish white streak; Metallic adamantine to submetallic luster; refractive index 2.622; optically biaxial.
IMA symbol Brk, grandfathered status — known before the IMA’s founding, named in 1825.
An accessory mineral in alpine veins in gneiss and schist; in contact metamorphic zones and hydrothermal veinlets; a common detrital mineral.
It is found associated with Anatase, rutile, titanite, orthoclase, quartz, hematite, calcite, chlorite, muscovite.
The name refers to Henry James Brooke (1771–1857), English crystallographer and mineralogist.
Collections: Collector Favorites.