Tennantite
Tennantite is the arsenic series of the tetrahedrite group: 8 IMA species, tennantite-(Fe) to -(Zn). Hardness 3 to 4.5, density 4.62; the sheet analyses read.
Tennantite is the arsenic series of the tetrahedrite group: a copper arsenic sulfosalt, hardness 3 to 4.5, density 4.62, in tetrahedral crystals to 20 cm, with Cornwall as type locality. Since 2019 the bare name is not a species; the IMA list has 8 tennantite rows, and the dominant divalent metal, such as iron or zinc, sets the suffix.
In short
- A series, not one species. Biagioni et al. 2020, American Mineralogist 105, 109–122 divides the tetrahedrite group into five series, tennantite among them, and makes the dominant charge-compensating constituent explicit with a suffix in brackets. The September 2026 IMA-CNMNC Master List has 8 tennantite rows: -(Cd), -(Cu), -(Fe), -(Hg), -(In), -(Mn), -(Ni) and -(Zn).
- The suffix reading. Both analyses on the Handbook of Mineralogy tennantite sheet read as zinc-dominant: Molly Gibson mine, Colorado, Zn 1.75 against Fe 0.12; San Lorenzo mine, Chile, Zn 1.43 against Fe 0.41. Arsenic is 99.5% and 65.3% of the semimetal. On those numbers both are nearer tennantite-(Zn) than -(Fe), a first-pass reading, not a determination.
- The sheet’s ideal formula is now a species of its own. The sheet’s ideal column, Cu12As4S13, works out at Cu 51.56%, As 20.26%, S 28.18%, exactly as printed. That is the composition of tennantite-(Cu), Cu6(Cu4Cu2)As4S13, approved in 2020 (2020-096, Peru).
- In the hand. Cubic, tetrahedral crystals, metallic, flint-grey to iron-black, hardness 3 to 4.5, no cleavage printed. A 20.00 g piece reads 15.67 g in water against tetrahedrite’s 15.98 g. The suffix needs an analysis; the old-label table is on tetrahedrite.
- Arsenic. Tennantite-(Fe) is 20.48% arsenic by mass, worked. This page gives no handling guidance; see is orpiment toxic for the regulatory sources. This is not health, safety or legal advice.
| Material | Formula (source) | As share of semimetal | Divalent metals (apfu) | Reads as, first pass | As by mass | Cu by mass |
|---|---|---|---|---|---|---|
| Molly Gibson mine, Aspen, Colorado (sheet analysis 1) | (Cu9.36Ag2.11Zn1.75Fe0.12Pb0.07)Σ13.41(As3.82Sb0.02)S13 | 99.5% | Zn 1.75, Fe 0.12 | Tennantite-(Zn); Ag 2.11, short of argento- | 17.18% analysed | 35.72% analysed |
| San Lorenzo mine, Santiago, Chile (sheet analysis 2) | (Cu10.17Zn1.43Fe0.41Ag0.01)Σ12.02(As2.58Sb1.37)S13 | 65.3% | Zn 1.43, Fe 0.41 | Tennantite-(Zn), with 34.7% Sb | 12.57% analysed | 42.05% analysed |
| Sheet ideal column (3) | Cu12As4S13 | 100% | None (Cu only) | Composition of tennantite-(Cu) | 20.26% | 51.56% |
| Tennantite-(Fe) | Cu6(Cu4Fe2)As4S13; Rd, 2019 s.p., United Kingdom | 100% | Fe 2 | - | 20.48% | 43.42% |
| Tennantite-(Zn) | Cu6(Cu4Zn2)As4S13; Rd, 2019 s.p., Switzerland | 100% | Zn 2 | - | 20.21% | 42.86% |
| Tennantite-(Cu) | Cu6(Cu4Cu2)As4S13; A, 2020-096, Peru | 100% | Cu at C | - | 20.26% | 51.56% |
| Argentotennantite-(Zn) | Ag6(Cu4Zn2)As4S13; Rd, 2019 s.p., Kazakhstan | 100% | Zn 2 | Needs Ag dominant in the A site | 17.14% | 14.54% |
| Tetrahedrite-(Fe), comparator | Cu6(Cu4Fe2)Sb4S13; Rd, 2019 s.p., Italy | 0% | Fe 2 | Antimony series | 0 | 38.49% |
What is tennantite? The arsenic series of the tetrahedrite group
Tennantite names the arsenic series of the tetrahedrite group; the species are tennantite-(Fe), tennantite-(Zn) and six others with a suffix. The abstract of Biagioni et al. 2020, American Mineralogist 105, 109–122, the report based on the IMA-CNMNC voting proposal approved in April 2019, writes the group formula M(2)A6M(1)(B4C2)X(3)D4S(1)Y12S(2)Z, with D = Sb3+, As3+, Bi3+ or Te4+, and divides the group into five series on the A, B, D and Y constituents: tetrahedrite, tennantite, freibergite, hakite and giraudite. The dominant C constituent, the charge-compensating one, is made explicit by a hyphenated suffix in brackets. Its first page calls the group the most common sulfosalts in many types of hydrothermal ore deposits.
What the IMA list holds. A scan of the September 2026 list finds 11 lines containing tennantite: tennantite-(Cd), -(Cu), -(Fe), -(Hg), -(In), -(Mn), -(Ni) and -(Zn), plus argentotennantite-(Fe), argentotennantite-(Zn) and kenoargentotennantite-(Fe). Tennantite-(Fe) and tennantite-(Zn) are marked Rd, redefined, 2019 s.p.; the other six are new approvals from 2020 to 2023. Every one of the eight has As4S13; seven have the shape Cu6(Cu4M2)As4S13, and tennantite-(In) is written Cu6(Cu5In)As4S13.
What the Handbook sheet describes. The Handbook of Mineralogy tennantite sheet predates the split and writes the group formula (Cu,Ag,Zn,Fe)12As4S13, Tetrahedrite group, forms a series with tetrahedrite. It gives cubic, tetrahedral crystals as large as 20 cm, commonly massive; twin plane {111}, contact and penetration twins commonly repeated; hardness 3 to 4.5, density 4.62. It prints no cleavage. Colour flint-grey to iron-black, cherry-red in transmitted light; in polished section grey inclining to black to brown to cherry-red, the last with high As and low Fe.
Which tennantite do I have? The suffix reading, worked
The suffix reading: in an analysis, take the semimetal first and the dominant divalent metal second; on the sheet’s own two analyses, both read zinc. The tennantite sheet prints two analyses with their atoms per formula unit on 13 sulfur. Molly Gibson mine, Aspen, Colorado: arsenic 3.82 against antimony 0.02, so arsenic is 99.5% of the semimetal; zinc 1.75 against iron 0.12. San Lorenzo mine, Santiago, Chile: arsenic 2.58 against antimony 1.37, 65.3% arsenic; zinc 1.43 against iron 0.41. Recomputed from the weight percentages on standard atomic weights, the atoms agree with the printed figures to within 0.02.
What the reading gives. Both are in the arsenic series, and in both zinc is the largest of the divalent metals analysed, so a first pass reads tennantite-(Zn) for each, not tennantite-(Fe). The Molly Gibson analysis carries 13.65% silver, 2.11 atoms; even if all of it sat in the six A positions it would be short of the dominance an argento- name requires. The sheet’s third column, the ideal Cu12As4S13, works out at Cu 51.56%, As 20.26% and S 28.18%, the figures printed. That is the composition of tennantite-(Cu), approved in 2020, so the textbook ideal formula is now a named species and no longer the generic one.
Documented failure: why it is only a first pass. The report lets the C site hold Cu2+ and Cu+ as well as Zn2+, Fe2+, Hg2+, Cd2+ and Mn2+. A zinc-against-iron comparison cannot see copper on that site, and the Molly Gibson metals sum to 13.41 against an ideal 12. A determination needs the site-by-site allocation in the report; this page has read only its abstract and first page, and the abstract says different B and C combinations should be regarded as separate species. For a label, the practice on how to label and catalogue a mineral collection applies: keep the old label, add tennantite (series) with the locality, and add a suffix only from an analysis.
Tennantite or tetrahedrite? What the balance and the separator show
Tennantite is the lighter end of the series: 4.62 on its sheet against tetrahedrite’s 4.97, so a 20.00 g piece reads 15.67 g in water against 15.98 g. The method is on how to measure specific gravity at home. The gap of 0.31 g is real on clean pieces, but the sheet says the two form a series, and the San Lorenzo analysis, with a third of its semimetal as antimony, sits between them. The same table is used, with the cleavage comparison, on enargite; enargite reads 15.51 g. Whether the group counts as sulfosalts in the 2008 IMA sense is set out on is enargite a sulfosalt and not repeated here.
On a laboratory separator. USGS Open-File Report 99-529, Table 1 lists 3 tennantite samples: total range 0.70 to above 1.70 amp, best range above 1.70. Tetrahedrite, 5 samples, is above 1.70 in both columns. The general picture is on which minerals are magnetic.
Arsenic. Worked on the IMA formulas, tennantite-(Fe) is 20.48% arsenic and tennantite-(Zn) 20.21%. This page gives no handling guidance; the regulatory entries for arsenic are quoted on is orpiment toxic and the general note is toxic minerals in a collection. This is not health, safety or legal advice.
Where tennantite is found: Cornwall to Tsumeb
The sheet calls tennantite rarer than tetrahedrite and gives Cornwall as type locality. Its Distribution field: in England, Cornwall [TL], from a number of mines in Gwennap, Gwinear, Illogan, St. Just and elsewhere; an ore mineral in the Gortdrum mine, near Tipperary, Ireland; Freiberg, Saxony; Kupferberg-Rudelstadt, Silesia, Poland; the Lengenbach quarry, Binntal, Switzerland; Dzhezkazgan, Kazakhstan. In the USA, many Colorado localities including the Freeland mine, Idaho Springs, the Central City district, the Molly Gibson and other mines at Aspen, the Red Mountain district and the Champion Lode, Georgetown district; Butte, Montana. Concepción del Oro, Zacatecas, Mexico; Morococha and Quiruvilca, Peru; the El Teniente mine, Chile; Yaogonxian, Hunan, China; and Tsumeb, Namibia, for remarkable large crystals.
The type locality on both sources. The IMA row for tennantite-(Fe) gives United Kingdom as the country of first description, which agrees with the sheet’s Cornwall [TL]; tennantite-(Zn) is given as Switzerland. The Cornwall locality page covers the county. The sheet names the mineral for Smithson Tennant (1761–1815), English chemist.
Company it keeps. The association line reads Cu–Pb–Zn–Ag sulfides and sulfosalts, pyrite, calcite, dolomite, siderite, barite, fluorite and quartz. The antimony end is on tetrahedrite and the cogwheel sulfosalt on bournonite. The reference section is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.