The most obvious physical properties of chalcopyrite are its brassy yellow color, metallic luster, and high specific gravity. These give it a similar appearance to pyrite and gold. Distinguishing these minerals is easy. Gold is soft, has a yellow streak and has a much higher specific gravity. Chalcopyrite is brittle and has a greenish gray streak. Pyrite is hard enough that it cannot be scratched with a nail, but chalcopyrite is easily scratched with a nail.

The name “fool’s gold” is most often associated with pyrite because it is more common and more often confused with gold. Chalcopyrite is also confused with gold, so the name “fool’s gold” is also applied and appropriate.

Physical Properties of Chalcopyrite
Chemical Classification	Sulfide
Color	Brass yellow. Tarnishes to gray green, sometimes iridescent.
Streak	Greenish black
Luster	Metallic
Diaphaneity	Opaque
Cleavage	Poor
Mohs Hardness	3.5 to 4
Specific Gravity	4.1 to 4.3
Diagnostic Properties	Color, greenish streak, softer than pyrite, brittle.
Chemical Composition	Copper iron sulfide, CuFeS2.
Crystal System	Tetragonal
Uses	The most important ore of copper for thousands of years.