Chalcopyrite

Chemical Formula : CuFeS₂
Hardness : 3.5-4
Cleavage : Two; usually distinct
Luster : Metallic
Color : Brass-yellow which is commonly tarnished to a slight iridescence.
Streak : Greenish-black
Density : 4.1-4.3
Diagnostic Features and Trivia : The tarnishing of chalcopyrite makes it appear like a rock that has been spray painted gold.
Crystal System and Habit : Tetragonal; tetrahedral
Twinning : {112} as contact, penetration or lamellar.
Polymorphs : None
Index of Refraction : Opaque