Brookite
Orthorhombic titanium dioxide polymorph, rare and photocatalytic.
Brookite is the orthorhombic polymorph of titanium dioxide (TiO2), one of four known natural forms of the mineral, alongside akaogiite, anatase, and rutile. It is named after English crystallographer and mineralogist Henry James Brooke, and is noted for its rarity compared to anatase and rutile, as well as its photocatalytic activity. Brookite crystals are typically brown, tabular, and elongated, with a submetallic luster and high refractive indices exceeding that of diamond.
- crystal_system
- Orthorhombic
- formula
- TiO2
- hardness
- 5+1⁄2 to 6 (Mohs)
- specific_gravity
- 4.08 to 4.18
- refractive_index
- Above 2.5 (biaxial positive)
- common_impurities
- Iron, tantalum, niobium
- type_locality
- Twll Maen Grisial, Fron Olau, Prenteg, Gwynedd, Wales
Lore & Background
The mineral occurs as an accessory in alpine veins in gneiss and schist, and is also a common detrital mineral.
Reader's Guide
Brookite is significant as a rare polymorph of titanium dioxide, exhibiting photocatalytic activity similar to anatase and rutile but with a larger unit cell volume (8 TiO2 groups per cell). Its structure consists of distorted octahedra sharing three edges, forming an orthorhombic lattice. The mineral's high refractive indices (above 2.5) and biaxial positive optical character make it distinctive among minerals. Brookite is typically brown, with weak pleochroism, and is brittle with a hardness of 5+1⁄2 to 6. Common impurities include iron, tantalum, and niobium. A variety known as arkansite occurs in Magnet Cove, Arkansas, and the Murun Massif in Eastern Siberia. Associated minerals include anatase, rutile, titanite, quartz, and hematite.
Did You Know?
- Brookite has a larger cell volume than anatase or rutile, with 8 TiO2 groups per unit cell.
- It is named after Henry James Brooke, an English crystallographer and wool trader.
- A variety called arkansite is found in Magnet Cove, Arkansas, and the Murun Massif in Siberia.
More in Minerals & Crystals 1-24
Elsewhere in the Minerals & Crystals universe
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record