Is enargite a sulfosalt?
Not a classic one. The 2008 IMA sulfosalt report centres on As3+, Sb3+, Bi3+ and Te4+; charge balance on Cu3AsS4, hardness 3, gives As5+. Its sheet never says.
Not a classic one. The 2008 IMA sulfosalt sub-committee report focuses on sulfosalts whose semimetal is As3+, Sb3+, Bi3+ or Te4+. Enargite, Cu3AsS4, hardness 3, balances only with arsenic at +5 when copper is Cu+ and sulfur S2−. The report also gives an extended definition that we could not read, so a broader yes is not ruled out.
In short
- What the report says, as far as we could read it. The 2008 IMA sulfosalt sub-committee report abstract says that, after an extended chemical definition of sulfosalts, attention is focused on classic sulfosalts with As3+, Sb3+, Bi3+ or Te4+ as cations, general formula (Me+, Me’2+, etc.)x [(Bi, Sb, As)3+, Te4+]y [(S, Se, Te)2−]z, and that it reviews more than 220 valid species in six main sub-groups. Only the abstract and first page could be fetched.
- The valence check. Assume Cu+, Ag+, Fe2+, Zn2+, Pb2+ and S2−, and solve each IMA formula for the semimetal. Cu3AsS4 gives arsenic +5, for enargite and luzonite alike; famatinite, Cu3SbS4, antimony +5. Tennantite-(Fe), tetrahedrite-(Fe), bournonite, sinnerite, proustite and pyrargyrite all give +3, the charge in the report’s classic formula. Enargite is the odd one out.
- What the sheet and the IMA list say. The Handbook of Mineralogy enargite sheet never uses the word sulfosalt and prints no mineral group. The tetrahedrite sheet calls tetrahedrite one of the most common of the sulfosalts. The luzonite and famatinite sheets put enargite’s dimorph and its antimony analogue in the stannite group, with stannite. The September 2026 IMA-CNMNC Master List has no class column and no line containing sulfosalt or sulphosalt.
- Documented failure: the arithmetic. The same check gives iron +5 for idaite, Cu3FeS4, tin +5 for kuramite, Cu3SnS4, and arsenic +1 for lautite, CuAsS. Those are not ordinary charges for iron or tin, so copper as Cu+ is an assumption that can fail. The check shows that enargite does not fit the classic formula as written; it does not measure an oxidation state.
- So what goes on the label? Enargite, Cu3AsS4. If a classification line is wanted, copper arsenic sulfide is what the formula supports. Sulfosalt in the broad sense is not ruled out by anything fetched here; classic sulfosalt, in the report’s As3+ sense, does not fit the arithmetic.
| Name | Formula (IMA), status | Semimetal, formal charge | In the abstract’s classic list (As3+, Sb3+, Bi3+, Te4+)? | Handbook group | Handbook says sulfosalt? |
|---|---|---|---|---|---|
| Enargite | Cu3AsS4; G, 1850 | As +5 | No | None printed | No |
| Luzonite | Cu3AsS4; G, 1874 | As +5 | No | Stannite group | No (associates include silver sulfosalts) |
| Famatinite | Cu3SbS4; G, 1873 | Sb +5 | No | Stannite group | No |
| Tennantite-(Fe) | Cu6(Cu4Fe2)As4S13; Rd, 2019 s.p. | As +3 | Yes | Tetrahedrite group (tennantite sheet) | Associates: sulfides and sulfosalts |
| Tetrahedrite-(Fe) | Cu6(Cu4Fe2)Sb4S13; Rd, 2019 s.p. | Sb +3 | Yes | Tetrahedrite group (tetrahedrite sheet) | Yes: one of the most common of the sulfosalts |
| Bournonite | CuPbSbS3; G, 1805 | Sb +3 | Yes | None printed | No |
| Proustite | Ag3AsS3; G, 1832 | As +3 | Yes | None printed | No |
| Pyrargyrite | Ag3SbS3; G, 1831 | Sb +3 | Yes | None printed | By implication: associates include other silver sulfosalts |
| Sinnerite | Cu6As4S9; A, 1964-020 | As +3 | Yes | No sheet used | No sheet used |
| Lautite | CuAsS; G, 1881 | As +1 (check fails) | No | No sheet used | No sheet used |
| Idaite | Cu3FeS4 | Fe +5 (check fails) | Not a semimetal | No sheet used | No sheet used |
| Kuramite | Cu3SnS4 | Sn +5 (check fails) | Not a semimetal | No sheet used | No sheet used |
Is enargite a sulfosalt? What the 2008 IMA report says
The 2008 report focuses on sulfosalts whose arsenic, antimony or bismuth is trivalent, and enargite’s formula does not balance that way. Moëlo et al. 2008, Sulfosalt systematics: a review (European Journal of Mineralogy 20, 7–46) is the report of the sulfosalt sub-committee of the IMA Commission on Ore Mineralogy, working with the CNMNC. Its abstract says Part I gives generalities of sulfosalt definition and nomenclature; that after an extended chemical definition of sulfosalts, attention is focused on classic sulfosalts with As3+, Sb3+, Bi3+ or Te4+ as cations, corresponding to the general formula (Me+, Me’2+, etc.)x [(Bi, Sb, As)3+, Te4+]y [(S, Se, Te)2−]z; and that Part II distinguishes six main crystal-chemical sub-groups, plus some unclassified species, covering more than 220 valid mineral species.
What we could not read. Only the publisher’s abstract page and the one-page preview were available; the body of the report was not. This page therefore does not say what the extended chemical definition contains, whether it names enargite, or where, if anywhere, its sub-groups place it. The first page prints the citation as European Journal of Mineralogy 2008, 20, 7–46; the publisher’s web page lists pages 7–62.
What the reference sheets say. The Handbook of Mineralogy enargite sheet gives Cu3AsS4, orthorhombic, hardness 3, density 4.45, perfect {110} cleavage, and prints no mineral group and no use of the word sulfosalt. The tetrahedrite sheet opens its Distribution field: one of the most common of the sulfosalts. The luzonite sheet, for enargite’s dimorph, gives stannite group. The species facts are on enargite.
Why enargite does not fit: the valence check
The valence check: with copper as Cu+ and sulfur as S2−, arsenic in Cu3AsS4 must be +5, outside the report’s classic list. Method: take each formula exactly as the September 2026 IMA list prints it, assign Cu+, Ag+, Fe2+, Zn2+ and Pb2+ to the metals and S2− to sulfur, and solve for the one remaining element. Enargite: three Cu+ give +3, four S2− give −8, so arsenic is +5. Luzonite, the same formula, is +5; famatinite, Cu3SbS4, gives antimony +5.
Against the classic examples. Tennantite-(Fe), Cu6(Cu4Fe2)As4S13: ten Cu+ and two Fe2+ give +14, thirteen S2− give −26, so four arsenic share +12, each +3. Tetrahedrite-(Fe) gives antimony +3; bournonite, CuPbSbS3, +3; proustite, Ag3AsS3, and pyrargyrite, Ag3SbS3, +3; sinnerite, Cu6As4S9, +3. Every one fits the abstract’s (Bi, Sb, As)3+ formula; enargite, luzonite and famatinite do not. The tetrahedrite group is set out on tetrahedrite, and the cogwheel sulfosalt on bournonite.
Documented failure: when the arithmetic breaks. The same procedure gives iron +5 for idaite, Cu3FeS4, tin +5 for kuramite, Cu3SnS4, and arsenic +1 for lautite, CuAsS. Those are not ordinary charges for iron, tin or arsenic, which means the starting assumption, every copper as Cu+, does not hold for every copper sulfide. This page does not say what the true charges in those minerals are. It uses the check only to show that enargite does not fit the classic formula as written.
Enargite, luzonite and famatinite: the Cu3MS4 rows
Enargite shares its formula shape with five other IMA species, and the Handbook groups two of them with stannite. A field scan of the September 2026 IMA list, checked by a token scan, finds 6 rows of the shape Cu3MS4: enargite and luzonite (Cu3AsS4), famatinite (Cu3SbS4), sulvanite (Cu3VS4), idaite (Cu3FeS4) and kuramite (Cu3SnS4). The luzonite and famatinite sheets both give stannite group, the group of stannite, Cu2FeSnS4; the luzonite sheet says dimorphous with enargite and forms a series with famatinite.
What that does and does not show. A collector’s label that files enargite with the sulfosalts is following a broad usage this page cannot check against the report’s full text. A label that files it with copper sulfides follows its formula. Neither is wrong on the evidence fetched here; classic sulfosalt, in the report’s As3+ sense, is the one reading the arithmetic does not support.
Not a magnet question. is arsenopyrite magnetic already tables enargite’s USGS separator row among the arsenic minerals and is not repeated here. Enargite carries 19.03% arsenic by mass in the ideal formula; handling is not covered here, see toxic minerals in a collection; this is not health or safety advice.
How should an enargite label read?
Name first, formula second, class only where a source supports it. Enargite, Cu3AsS4, is the IMA name and formula, status G, 1850, Peru. The Handbook supports copper arsenic sulfide as a description by composition; the 2008 report’s abstract does not support classic sulfosalt; whether its extended definition makes enargite a sulfosalt in the broad sense is open on the sources fetched here.
Separating it from the true classic sulfosalts in the hand. Tennantite and tetrahedrite, both +3 on the check, have no cleavage on their sheets; enargite cleaves perfectly on {110}. That test, with in-water weights, is on enargite and is not repeated here. The method is on cleavage or fracture: how to tell.
Where to go next. The species pages for tetrahedrite, bournonite, proustite and pyrargyrite cover the classic examples in the table above. The classification guides are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.