rutile

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rutile (titanium dioxide, TiO2) Black to red-brown oxide mineral, found in igneous and metamorphic rocks and quartz veins. It occurs as long, prismatic crystals in the tetragonal system and as granular masses. It has a metallic lustre, is brittle and is used as a gemstone. Hardness 6–6.5; r.d. 4.2.

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