Rutile assumes tetragonal forms isomorphous with cassiterite, SnO 2 (and also zircon, ZrSiO 4); anatase is also tetragonal, and brookite or thorhombic. Rutile is the most stable and anatase the least, a character reflected in the decrease in density from rutile (4.2) and brookite (4.0) to anatase (3.9).
At Sao Joao da Chapada, in Minas Geraes, diamonds occur in a clay interstratified with the itacolumite, and are accompanied by sharp crystals of rutile and haematite in the neighbourhood of decomposed quartz veins which intersect the itacolumite.
Minute rods or needles of rutile are also common in slates, and well-formed cubes of pyrites are often visible on the splitting faces.
In diameter), with often felspar, tourmaline, zircon, epidote, rutile and more or less calcite.
At a red heat rutile is produced, at the boiling point of zinc brookite, and of cadmium anatase.
The commonest titanium mineral is rutile or titanium dioxide, T102; anatase and brookite are crystalline allotropes.