Titanium dioxide occurrence

Beydoun D, Amal R, Low G, McEvoy S (2002) Occurrence and prevention of photodissolution at the phase junction of magnetite and titanium dioxide. J Mol Catal A 180 (1) 193-200... 

Titanium Oxide 6 Complex Oxides Sulfide. The naturally occurring dioxide Ti02 has three crystal modifications, rutile, anatase, and brookite. In rutile, the commonest, the Ti is octahedral and this structure is a common one for MX2 compounds. In anatase and brookite there are very distorted octahedra of oxygen atoms about each titanium, two being relatively close. Although rutile has been assumed to be the most stable form because of its common occurrence, anatase is 8 to 12 kJ mol-1 more stable than rutile. 

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