Rutile (Rutilated Quartz)
(c) 2006 Andrew Alden, licensed to About.com, Inc. (fair use policy)
Rutile is the natural mineral form of titanium dioxide, TiO2, in plutonic and metamorphic rocks. It is generally dark red or metallic black. The name rutile comes the Latin for dark red. It forms prismatic crystals that can be thin as hairs, as in this specimen of rutilated quartz. Rutile readily forms twins and sprays of six or eight crystals. In fact, microscopic rutile needles account for the stars (asterism) in star sapphire.
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