Star Rutile is constituted by six ray star of oriented needles of fibrous
sagenitic yellow rutile. The star is usually overgrown above an hexagonal
blade crystal of hematite. It is a educational example of epitaxy, the
property of some minerals to grow a crystal of a particular orientation
on top of another crystal, where the orientation is determined by the underlying
crystal. The rutile follows the atomic lattice of the hematite, but with
changed composition. This is basically due to a consumed iron content in
the hydrothermal solution and a relative increase of titanium.
The material comes from Novo Horizonte, Bahia, Brazil. Formerly belonging
to Ibitiara municipality. Until the mid 1990's Ibitiara county was big
and Remedios and Novo Horizonte were districts of Ibitiara; then there
was a vote and Novo Horizonte was split from Ibitiara and became a new
county ("município"), and Remedios voted to join Novo Horizonte,
so now the only county that produces rutilated quartz and rutile on hematite
is Novo Horizonte, and Remedios is just a district of Novo Horizonte.
Full six harm stars are highly valuable and quite rare, while broken
stars with five or less arms are called "pés de galinha" (crow's-feet)
and are much less expensive.