Rutile, titanium oxide,
Rutile is a common mineral in igneous and metamorphic rocks. It is found in quartz veins where it frequently occurs as acicular crystal inclusions in quartz crystals. Rutile is polymorphous with anatase and brookite. It is a source of the metal titanium, used in the aircraft industry for its heat-resisting properties and is sometimes used as a semiprecious stone. Fine crystal specimens are found in Brazil, USA and Switzerland. Brazil is well known as the source of particularly attractive golden fan-like sprays of rutile crystals on hematite.
The picture shows a nice specimen of reticulated, brown, prismatic crystals of rutile on, and embedded in, quartz crystals . The specimen is from Minas Gerais, Brazil.