Is chalcopyrite a sulfide?
Yes: chalcopyrite is CuFeS2, a copper iron sulfide, 34.63% copper and 34.94% sulfur by mass, tetragonal rather than cubic, hardness 3.5–4. The one-to-one check.
Yes. Chalcopyrite is copper iron sulfide, CuFeS2, on the September 2026 IMA list: 34.63% copper, 30.43% iron and 34.94% sulfur by mass, no oxygen. It is tetragonal, not cubic, hardness 3.5 to 4. Of 11 IMA rows written in copper, iron and sulfur alone, it alone has a 1 : 1 : 2 ratio.
In short
- The verdict. Chalcopyrite is a sulfide. The September 2026 IMA-CNMNC Master List writes CuFeS2, status G; the Handbook of Mineralogy sheet writes the same and lists its associates as “sphalerite, galena, tetrahedrite, pyrite, many copper sulfides”. Worked, CuFeS2 is 34.63% copper, 30.43% iron and 34.94% sulfur, with no oxygen: the sulfur is bonded as sulfide, not sulfate. The geology.com chalcopyrite article gives its chemical classification as Sulfide.
- The one-to-one check. Two independent scans of the IMA list find 11 rows written in Cu, Fe and S alone. Chalcopyrite is the only one with copper equal to iron and metals equal to sulfur. Mooihoekite, Cu9Fe9S16, matches the first but not the second; cubanite, isocubanite, idaite and nukundamite match the second but not the first. Copper runs from 23.41% (cubanite) to 63.32% (bornite).
- Is chalcopyrite cubic? No. The sheet gives tetragonal, point group −42m, with equant, tetrahedral-shaped crystals. Its cell has a = 5.281 and c = 10.401 Å; twice a is 10.562, so c falls 1.52% short of a doubled cube. Cubic sphalerite, the sheet’s first associate, has a = 5.4060. A tetrahedral look does not make a cubic mineral.
- Documented failure: brass-yellow is not a name. Cubanite, CuFe2S3, is “brass-yellow to bronze-yellow” on its sheet, hardness 3.5, density 4.03–4.18: a 20.00 g piece reads 15.04–15.22 g in water against chalcopyrite’s 15.12–15.35 g. Colour, hardness and weight overlap. Its sheet prints “Strongly magnetic”; chalcopyrite’s prints no magnetic property.
- Not a sulfate, not pyrite. Copper sulfates such as antlerite, Cu3(SO4)(OH)4, carry four oxygens per sulfur and sit in the oxidized zone; chalcopyrite has none. pyrite is FeS2, cubic, hardness 6–6.5. The sheet derives the name from the Greek for brass and pyrite. Hazard questions go to toxic minerals in a collection; this is not advice.
| Mineral and IMA formula | IMA status | Cu, wt% | Fe, wt% | S, wt% | Cu : Fe | (Cu+Fe) : S | Sheet: colour, density, magnetism |
|---|---|---|---|---|---|---|---|
| Chalcopyrite, CuFeS2 | G, 1725 ? | 34.63 | 30.43 | 34.94 | 1 | 1 | Brass-yellow; 4.1–4.3; none printed |
| Cubanite, CuFe2S3 | G, 1843 | 23.41 | 41.15 | 35.44 | 0.5 | 1 | Brass-yellow to bronze-yellow; 4.03–4.18; “Strongly magnetic” |
| Isocubanite, CuFe2S3 | A, 1983 s.p. | 23.41 | 41.15 | 35.44 | 0.5 | 1 | — |
| Haycockite, Cu4Fe5S8 | A, 1971-028 | 32.18 | 35.35 | 32.47 | 0.8 | 1.125 | — |
| Putoranite, Cu1.1Fe1.2S2 | A, 1979-054 | 34.77 | 33.33 | 31.90 | 0.917 | 1.15 | — |
| Mooihoekite, Cu9Fe9S16 | A, 1971-019 | 36.03 | 31.66 | 32.31 | 1 | 1.125 | — |
| Talnakhite, Cu9Fe8S16 | A, 1967-014 | 37.34 | 29.17 | 33.49 | 1.125 | 1.0625 | — |
| Fukuchilite, Cu3FeS8 | A, 1967-009 | 37.90 | 11.10 | 50.99 | 3 | 0.5 | — |
| Idaite, Cu3FeS4 | G, 1958 | 50.87 | 14.90 | 34.22 | 3 | 1 | — |
| Nukundamite, Cu3.4Fe0.6S4 | A, 1978-037 | 57.19 | 8.87 | 33.94 | 5.667 | 1 | — |
| Bornite, Cu5FeS4 | A, 1962 s.p. | 63.32 | 11.13 | 25.56 | 5 | 1.5 | Copper-red to pinchbeck-brown, tarnishes iridescent purplish; 5.06–5.08; none printed |
Is chalcopyrite a sulfide? What the formula says
Yes: copper, iron and sulfur, and nothing else. The September 2026 IMA-CNMNC Master List lists chalcopyrite as CuFeS2, status G (grandfathered), with the year printed as 1725 ? and the country unknown. The Handbook of Mineralogy chalcopyrite sheet writes the same formula, puts it in the chalcopyrite group, calls it “a very common copper mineral” and lists its associates as sphalerite, galena, tetrahedrite, pyrite and “many copper sulfides”. With Cu 63.546, Fe 55.845 and S 32.06, the formula mass is 183.51: 34.63% copper, 30.43% iron and 34.94% sulfur, the sheet’s ideal column. There is no oxygen, so the sulfur is the sulfide anion rather than part of a sulfate group.
The specimen the sheet analysed. The Western mines, Vancouver Island, British Columbia, microprobe analysis prints Cu 35.03, Fe 31.00 and S 34.96, total 100.99, leading to Cu1.01Fe1.01S2.00. Recast by script to 2 sulfur, it gives Cu 1.011 and Fe 1.018, within 0.01 of the printed figures. These copper figures agree with is chalcopyrite the same as peacock ore and is copper a mineral; the lustre question for zinc sulfide is on is sphalerite a sulfide and is not repeated here.
How is chalcopyrite different from the other copper iron sulfides?
The one-to-one check, method. A script read the formula column of the September 2026 IMA list, with page-break characters stripped, and kept every row whose formula contains the element symbols Cu, Fe and S and no others. A second method, a token scan of each line, found the same 11: bornite, chalcopyrite, cubanite, fukuchilite, haycockite, idaite, isocubanite, mooihoekite, nukundamite, putoranite and talnakhite. The count is of formula shape on one list, not of every copper iron sulfide ever described.
Result. Chalcopyrite is the only row with copper equal to iron and metals equal to sulfur, 1 : 1 : 2. Mooihoekite has equal copper and iron but 18 metals to 16 sulfur; cubanite, isocubanite, idaite and nukundamite balance metals against sulfur but not copper against iron. By copper, chalcopyrite sits fourth from the bottom at 34.63%, above cubanite and isocubanite (23.41%) and haycockite (32.18%); bornite has the most, 63.32%. By sulfur only fukuchilite (50.99%), cubanite and isocubanite (35.44%) carry more than chalcopyrite’s 34.94%.
Documented failure: brass-yellow. The cubanite sheet gives brass-yellow to bronze-yellow, hardness 3.5 and density 4.03 to 4.18, where chalcopyrite is brass-yellow, 3.5 to 4 and 4.1 to 4.3. In water a 20.00 g piece reads 15.04 to 15.22 g as cubanite and 15.12 to 15.35 g as chalcopyrite: the ranges overlap. The two sheets differ in a way a hand test registers only on magnetism: cubanite’s prints “Strongly magnetic”, chalcopyrite’s prints nothing. The broader survey is on which minerals are magnetic.
Is chalcopyrite cubic or tetragonal?
Tetragonal, close to cubic proportions. The chalcopyrite sheet, read on the rendered page, gives tetragonal, point group −42m, space group I−42d, with “equant, tetrahedral-shaped crystals” to as large as 10 cm, sphenoidal {112} faces typically large, dull and striated parallel to [1−10], and {−112} faces small and bright. The cell is a = 5.281, c = 10.401 Å, Z = 4. Twice a is 10.562 Å, so c is 0.9848 of a doubled square base, 1.52% short. Cubic sphalerite, point group −43m, has a = 5.4060 Å; chalcopyrite’s a is 2.31% smaller.
Documented failure: the printed density. Worked from that cell, four CuFeS2 units in 290.07 ų give 4.202, against the sheet’s printed calculated density of 4.283. The same arithmetic reproduces cubanite’s printed 4.024 exactly. The measured 4.1 to 4.3 is used on this page and the sheet is not corrected. The tetrahedral habit and the 1.52% are reasons a chalcopyrite crystal looks like a cubic one; none makes it cubic.
Is chalcopyrite fool’s gold, natural, or a mineral?
Fool’s gold. The geology.com chalcopyrite article says the name is most often associated with pyrite, but that chalcopyrite is also confused with gold, so the name is also applied; the comparison is on what is fool’s gold. Copper pyrite? Chalcopyrite and pyrite are separate species: CuFeS2, tetragonal, hardness 3.5 to 4, against FeS2, cubic, 6 to 6.5. The chalcopyrite sheet derives the name from the Greek for brass and pyrite.
Natural, and a mineral. It has its own IMA row and forms in hydrothermal veins, stockworks, disseminations and massive replacements, by its sheet. Iridescent surfaces sold as peacock ore may be natural or acid-treated; geology.com says some souvenir shops sell acid-treated chalcopyrite under that name, and the test is on is chalcopyrite the same as peacock ore. A sulfide, not a sulfate. Copper sulfates such as antlerite and brochantite carry sulfur inside SO4 groups and form in oxidized zones; the same distinction for lead is on is anglesite a sulfate. The species page is chalcopyrite; more guides are in the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.