Chalcopyrite
CuFeS₂ · Tetragonal · also called copper pyrite, peacock ore
Chalcopyrite is the world's most important copper ore and the second most common cause of false gold reports. It is noticeably softer than pyrite, which is the quickest way to separate the two, and its tarnish colours are unmistakable once you have seen them.
Properties
- Mohs hardness
- 3.5–4
- Streak
- green black
- Lustre
- metallic
- Colour
- Deeper, brassier yellow than pyrite, often with a spectacular iridescent tarnish in purple, blue, and green. Material sold as 'peacock ore' is usually tarnished chalcopyrite or bornite.
- Cleavage
- Poor cleavage; specimens usually break irregularly.
- Fracture
- Uneven, brittle
- Specific gravity
- 4.1–4.3 (water = 1)
- Magnetism
- Not magnetic
- Acid test
- No reaction
- UV
- Not fluorescent
Tests that confirm chalcopyrite
- A steel nail scratches it easily — pyrite resists the same nail.
- Streak is greenish black.
- The iridescent film rubs away, revealing plain brass yellow underneath.
What chalcopyrite gets confused with
Each of these is settled by one test. Run that test first.
Where it is found
Hydrothermal veins and porphyry copper deposits; abundant on mine dumps in copper districts.
Is it worth anything?
Low value as specimens unless the crystals are sharp. Brightly tarnished 'peacock ore' sold in gift shops is often acid-treated to force the colours.