Is chalcopyrite the same as peacock ore
Sometimes. Peacock ore is a trade name for bornite and for acid-tarnished chalcopyrite. A fresh surface decides: brass-yellow chalcopyrite, copper-red bornite.
Sometimes. Peacock ore is a trade name, not a species: geology.com applies it to bornite, Cu5FeS4, and says brightly coloured material sold under it is frequently chalcopyrite, CuFeS2, tarnished with acid. A fresh surface decides: brass-yellow is chalcopyrite, hardness 3.5 to 4; copper-red to pinchbeck-brown is bornite, hardness 3 to 3.25.
In short
- Peacock ore names a surface, not a mineral. The geology.com bornite article says bornite is commonly called peacock ore or purple copper ore, and that material whose colours greatly exceed what is expected on bornite is frequently chalcopyrite intentionally tarnished with acid. So chalcopyrite is often what is sold as peacock ore, without being the same species as bornite.
- The fresh-break rule. The film is the colour, so look underneath it. The Handbook of Mineralogy gives chalcopyrite as brass-yellow and bornite as copper-red to pinchbeck-brown on fresh surfaces. That one observation chooses; the bornite species page covers the natural tarnish.
- Iridescence proves nothing about species. Of the 176 sheets in this site's reference set, 11 record iridescence in the Color field, among them pyrite, marcasite, covellite, hematite and stibnite as well as chalcopyrite and bornite.
- The 4.68 line. Chalcopyrite's density is 4.1 to 4.3 and bornite's 5.06 to 5.08. A clean 20.00 g piece weighs 15.12 to 15.35 g suspended in water as chalcopyrite and 16.05 to 16.06 g as bornite, 0.70 g apart at the closest. Hardness does not help: the gap is 0.25 of a Mohs point.
- Bornite carries nearly twice the copper. Cu5FeS4 is 63.32% copper by mass and CuFeS2 34.63%, worked from standard atomic weights. Chalcopyrite is also one of the minerals called fool's gold, which what is fool's gold sets out.
| Criterion | Chalcopyrite | Bornite | Does it choose? |
|---|---|---|---|
| Formula | CuFeS2 | Cu5FeS4 | Only by analysis |
| Copper by mass | 34.63% (the sheet's pure column also reads 34.63) | 63.32% (the sheet's pure column reads 63.33) | Only by analysis |
| Colour on a fresh surface | Brass-yellow | Copper-red to pinchbeck-brown | Yes: the fresh-break rule |
| Tarnish as recorded | May be tarnished and iridescent | Rapidly tarnishes iridescent purplish | No: both tarnish |
| Streak | Greenish black | Pale grayish black | Weakly |
| Hardness (Mohs) | 3.5 to 4 | 3 to 3.25 | No: 0.25 point apart |
| Density, measured | 4.1 to 4.3 | 5.06 to 5.08 | Yes on clean material: cut-off 4.68 |
| 20.00 g piece, weight in water | 15.12 to 15.35 g | 16.05 to 16.06 g | Yes on a 0.01 g scale |
| Crystal system; largest crystals | Tetragonal; tetrahedral-shaped, to 10 cm | Orthorhombic, pseudocubic; to 6 cm | Yes, when crystals are present |
| IMA status (Sept 2026) | Grandfathered | Approved, 1962 s.p. | - |
Is chalcopyrite the same as peacock ore? What the name covers
Peacock ore is a trade name for an iridescent surface, and two species arrive under it. The geology.com bornite article says bornite is commonly called peacock ore or purple copper ore after its iridescent tarnish, and that some material sold as peacock ore has a tarnish greatly exceeding what is expected on bornite: this material is frequently chalcopyrite that has been intentionally tarnished with acid. Its chalcopyrite article says the same from the other side, and adds that peacock ore is a more appropriate name for bornite. This page gives no acid procedure.
The two species, as the Handbook of Mineralogy prints them. Chalcopyrite is CuFeS2, tetragonal, brass-yellow, may be tarnished and iridescent, hardness 3.5 to 4, density 4.1 to 4.3; its name is from the Greek for brass and pyrite. Bornite is Cu5FeS4, orthorhombic and pseudocubic, copper-red to pinchbeck-brown on fresh surfaces and rapidly tarnishes iridescent purplish, hardness 3 to 3.25, density 5.06 to 5.08. The IMA-CNMNC list of minerals lists both as species. Both formulas are the same on the two sources.
Copper content, worked. With Cu 63.546, Fe 55.845 and S 32.06, CuFeS2 has a formula mass of 183.51 and is 34.63% copper, the figure the chalcopyrite sheet prints for pure CuFeS2. Cu5FeS4 has a mass of 501.82 and is 63.32% copper; the bornite sheet's pure column reads 63.33, a rounding difference. The Superior, Arizona, bornite analysis on the sheet reads 62.99%.
The fresh-break rule: brass-yellow or copper-red
Under the tarnish, chalcopyrite is brass-yellow and bornite is copper-red to pinchbeck-brown, and that is the test that chooses. Once a film is present, the film is the colour, so a useful check has to reach unfilmed mineral: a broken corner, the underside, an edge hidden by matrix. The decision rule, stated once: brass-yellow underneath is chalcopyrite; copper-red to bronze-brown underneath is bornite. The chalcopyrite species page is at chalcopyrite.
Where it fails. The bornite sheet says it tarnishes rapidly, so an old break on a bornite may already be dark, and a fresh one is needed. A specimen with no exposed interior at all needs a second test, and hardness is not it: 3.5 to 4 against 3 to 3.25 is a quarter of a Mohs point, closer than a pocket test resolves. Streak helps a little, greenish black against pale grayish black, on an inconspicuous spot; the technique is on how to use a streak plate.
Weighing works where the material is clean. At 4.1 to 4.3, a 20.00 g piece of chalcopyrite has a volume of 4.88 to 4.65 cm³ and weighs 15.12 to 15.35 g suspended in water; at 5.06 to 5.08 bornite weighs 16.05 to 16.06 g. The midpoint of 4.3 and 5.06 is 4.68. Matrix, quartz or mixed sulphides pull the figure toward the matrix, so a souvenir lump with rock attached gives an answer about the lump. The method is on how to measure specific gravity at home.
How many minerals tarnish iridescent? 11 of 176 sheets
Iridescence is recorded in the Color field of 11 of the 176 Handbook sheets in this site's reference set, so a peacock surface narrows the field without choosing a species. Method: the 176 sheets were converted with pdftotext -layout, the Color field was cut out by regular expression and searched case-insensitively for iridesc; the same 11 are the only sheets that use the word anywhere. They are bornite, chalcopyrite, covellite, hematite, labradorite, marcasite, orthoclase, pyrite, pyrrhotite, skutterudite and stibnite. In two of them, labradorite and orthoclase, it is an optical play of colour rather than a tarnish.
The sulphides in that list are the ones to rule out. Pyrite tarnishes darker and iridescent and is hardness 6 to 6.5, far harder than either peacock species; covellite is commonly highly iridescent but indigo-blue underneath, at hardness 1.5 to 2. Chalcopyrite's own sheet uses the word may: an untreated chalcopyrite can carry a natural iridescent film, so a coloured chalcopyrite is not proof of treatment either.
Who the answer bornite is wrong for: anyone whose piece is brass-yellow on a fresh break, whatever the surface looks like. Who the answer chalcopyrite is wrong for: anyone holding copper-red to bronze material that is heavy for its size. Who neither answer suits: an intergrowth of both, which the bornite sheet makes plausible by listing chalcopyrite first among its associates, and which deserves a label naming both. The identification guides are indexed at the collecting guides and the species in the species index. Nothing here is offered for sale; the wanted list is the only commercial route.