Brookite

Brookite is a naturally occurring orthorhombic crystalline form of titanium dioxide. It is one of the mineral’s three principal polymorphs, alongside rutile and anatase.

Titanium dioxide: Titanium dioxide is an inorganic compound composed of titanium and oxygen, with several crystalline forms. Brookite is one crystalline form of this compound.
Polymorphism (materials science): Polymorphism is the ability of a solid chemical substance to crystallize in more than one structure. Brookite, anatase, and rutile are structurally different forms of the same compound.
Henry James Brooke: Henry James Brooke was an English mineralogist and crystallographer active in the early nineteenth century. Brookite was named in his honor.
Photocatalysis: Photocatalysis uses light-activated materials to accelerate chemical reactions. Brookite is studied as a photocatalyst and as a component in mixed-phase titanium dioxide.
Orthorhombic crystal system: The orthorhombic crystal system has three mutually perpendicular axes of unequal length. Brookite crystals belong to this crystal system.
Phase transition: A phase transition is a change between distinct physical states or structural phases of matter. Heating can transform brookite into other titanium dioxide polymorphs.
Arthurs Seat: Arthur’s Seat is an extinct volcano overlooking Edinburgh, Scotland. Brookite was first described from specimens found at this locality.
Water splitting: Water splitting uses energy to separate water into hydrogen and oxygen. Brookite-containing photocatalysts are investigated for solar-driven hydrogen production.
Crystal structure: A crystal structure describes the ordered arrangement of atoms, ions, or molecules in a crystalline solid. Brookite’s orthorhombic symmetry comes from its atomic arrangement.
Metastability: Metastability is a condition in which a system persists in a state that is not its lowest-energy equilibrium state. Brookite can persist despite rutile being the stable form under ordinary conditions.

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Rutile structureCompared with: It provides a third naturally occurring TiO₂ structure for comparison.