Brookite is one of the three main polymorph forms of TiO2, three minerals
with the same composition but different structure, rutile and anatase being
the other two.
Brookite is the most rare of the three and usually occurs in very fragile
crystals of a nice red colour with a refractive index higher than diamond.
Is a typical mineral of alpine type hydrothermal vein and for this reason
is often included in quartz. In this case quartz preserve its beauty and
its fragility. Most of the brookite included in quartz is strictly associated
with rutile, often of silver colour, more rarely golden. The association
is a clear epitaxy with rutile needles crossing the brokite blade with
an angle of 60 degres. So the brookite crystal is often masked by the rutile
fibers and quite rarely it appear rutile free.
Main deposit of cutting quartz material with brookite inclusions comes
from the area of Diamantina, Jequitinhonha Valley, between Gouveia and
Corinto, in Minas Gerais, Brazil. Also good brookites in quartz have appeared
on the market from Pakistan, but the production is more directed to collector
crystal than to cutting rough.
Left: Brookite and silver Rutile from Brazil. Right: Brookite and golden