Rutile (ROO-tle or ROO-tile) is generally dark red or metallic black and has a Mohs hardness of 6 to 6.5. The name rutile comes from 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.
Rutile is the natural mineral form of titanium dioxide, TiO2, in plutonic and metamorphic rocks. (more below)
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