Rutile

Chemical Formula : TiO₂
Hardness : 6-6.5
Cleavage : Two, distinct to good
Luster : Andamantine to metallic
Color : White in pure specimens, but impurities often make it reddish brown, but can be yellowish, blusih, or black.
Streak : White for pure specimens, but those with impurities are pale brown to grayish black.
Density : 4.25
Diagnostic Features and Trivia : Rutile can be found as inclusions in quartz, mica, and corundum.
When found quartz crystals, the rutile often resembles strands of golden hair frozen in the crystal. Linear groups od rutile inclusions produce the cat's eye varieties of corundum, and cyclic twins create the star effect in others. Crystal System and Habit : Tetragonal; commonly prismatic to slender to acicular terminating in dipyramids {101} or {111}.
Twinning : Veryy comon on {101}; simple contact, repeated contact twins give geniculate forms or cyclic twins with six or eight individuals.
Polymorphs : Anatase, and Brookite
Index of Refraction : omega=2.065-2.616; epsilon=2.890-2.903