Page "Armalcolite" Paragraph 12

The crystal structure of armalcolite is close to that of distorted brookite.

It is based on deformed octahedra with a titanium atom in the center and six oxygen atoms at the corners.

Magnesium or iron ions are located in the interstitial sites ; they do not contribute significantly to the lattice framework, which is held by Ti-O bonds via the corners of the octahedra.

However, these ions affect optical properties rendering the mineral opaque in contrast to the transparent titanium dioxide TiO < sub > 2 </ sub >.