Chalcopyrite
Chalcopyrite is copper iron sulfide, CuFeS2, and the single most important ore mineral of copper worldwide. It crystallizes in the tetragonal system, usually as tarnished brassy-yellow masses or small tetrahedral-looking crystals in hydrothermal veins. Its softness relative to pyrite and its greenish-black streak are the quickest ways to separate it from that more famous fool's-gold mineral.
Chalcopyrite properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | CuFeS2 |
| Mohs hardness | 3.5–4 |
| Crystal system | Tetragonal |
| Luster | Metallic |
| Streak | Greenish black |
| Cleavage | Poor, indistinct |
| Fracture | Uneven to conchoidal |
| Specific gravity | 4.1–4.3 |
| Transparency | Opaque |
| Common colors | Brass yellow, Golden yellow, Iridescent tarnish |
| Rarity | common |
Geology & background
Chalcopyrite precipitates from hydrothermal fluids in a wide range of settings, including porphyry copper deposits, volcanogenic massive sulfide deposits on the seafloor, and simple hydrothermal veins, commonly alongside pyrite, sphalerite, and galena. Because it supplies the majority of the world's mined copper, it is economically far more significant than its modest price as a mineral specimen would suggest, and major deposits in Chile, the United States, and Zambia have driven copper production for over a century. Collectors prize crystallized specimens showing sharp tetragonal faces or an iridescent surface tarnish, sometimes marketed as peacock ore, though that colorful tarnish is more typically associated with the related mineral bornite.
Weathering of chalcopyrite near the surface produces secondary copper minerals such as malachite and azurite, which is often how prospectors first locate a buried sulfide deposit.
How to identify Chalcopyrite
Chalcopyrite shows a brassy to golden yellow color with a metallic luster, often dulled by an iridescent blue, purple, or green tarnish. Its streak is greenish black to black, distinguishing it immediately from pyrite's greenish-black-to-brownish streak on unglazed porcelain and from gold, which streaks yellow and is far denser and malleable. Hardness of 3.5 to 4 makes it noticeably softer than pyrite, which will scratch it, and chalcopyrite crystals are typically smaller and less well-formed than pyrite's classic cubes.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Chalcopyrite is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Chalcopyrite worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Chalcopyrite supplies a larger share of the world's mined copper than any other single mineral.
- Its softness allows a steel knife to scratch it easily, a simple test that separates it from harder pyrite.
- The iridescent rainbow tarnish often sold as peacock ore is more commonly produced by the related copper mineral bornite.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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