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In some crystals, e.g. brookite, the optic axes for red light and for blue light may be, at certain temperatures, in planes at right angles.

Minute crystals of brookite have been detected with anatase and rutile in the iron-ore of Cleveland in Yorkshire.

Crystals of brookite, as well as of anatase and rutile, have been prepared artificially by the interaction of steam and titanium fluoride, the particular modification of titanium dioxide which results depending on the temperature at which the reaction takes place.

The two latter are tetragonal in crystallization, whilst brookite is orthorhombic.

Two types of brookite crystals may be distinguished.