Tetrahedrite
Tetrahedrite is hardness 3 to 4.5 and density 4.97, with tetrahedral crystals to 15 cm. Since 2019 it is a group of 34 species and the bare name is retired.
Tetrahedrite is a copper antimony sulphosalt of the tetrahedrite group, hardness 3 to 4.5, density 4.97, flint-grey to iron-black with tetrahedral crystals to 15 cm. Since the 2019 redefinition it is no longer a species name: the September 2026 IMA list holds 34 valid group species and not one of them is called plain tetrahedrite. Old labels name a group, not a mineral.
In short
- Plain tetrahedrite has not been a species since 2019. The September 2026 IMA-CNMNC Master List holds 34 valid tetrahedrite-group species and none is called tetrahedrite, tennantite or freibergite. The seven antimony-dominant ones are tetrahedrite-(Fe), -(Zn), -(Cu), -(Cd), -(Hg), -(Mn) and -(Ni).
- The commonest two are tetrahedrite-(Fe) and tetrahedrite-(Zn), both redefined in 2019 rather than newly discovered, with type localities in Italy and Germany respectively. A specimen labelled tetrahedrite is almost certainly one of those two, but almost certainly is not a determination.
- Tennantite-(Fe) has a United Kingdom type locality, redefined 2019, which makes the arsenic side of this group a British species as well as a Cornish mining commonplace. The bare name tennantite is equally retired.
- Nothing you can do in the hand tells you which species you have. Hardness spans 3 to 4.5, density 4.97 for the antimony end and 4.62 for the arsenic end, and both are opaque and metallic. The suffix is an electron-microprobe result, not an observation.
- The habit is the diagnostic feature, and it is in the name. The Handbook records tetrahedral crystals to 15 cm, commonly as parallel groups and as contact or penetration twins on {111}. Nothing else a collector meets at that hardness and lustre grows tetrahedra.
| Label on the specimen | Status now | Valid species it could be | How many |
|---|---|---|---|
| Tetrahedrite | Retired 2019 | tetrahedrite-(Cd), -(Cu), -(Fe), -(Hg), -(Mn), -(Ni), -(Zn) | 7 |
| Tennantite | Retired 2019 | tennantite-(Cd), -(Cu), -(Fe), -(Hg), -(In), -(Mn), -(Ni), -(Zn) | 8 |
| Freibergite | Retired 2019 | argentotetrahedrite-(Cd), -(Fe), -(Hg), -(Zn) and the two kenoargentotetrahedrites | 6 |
| Names with no common old equivalent | — | The argentotennantites, hakites, giraudite-(Zn), the rozhdestvenskayaites and kenoargentotennantite-(Fe) | 10 |
| Goldfieldite | Still valid | goldfieldite, plus arsenogoldfieldite and stibiogoldfieldite | 3 |
| Whole group | — | All tetrahedrite-group species on the September 2026 list | 34 |
What the 2019 redefinition actually did
The tetrahedrite group is a solid solution with two substituting sites, and for most of its history the species names tracked the dominant metalloid — antimony for tetrahedrite, arsenic for tennantite — while the metal content was left as a variety adjective. The 2019 nomenclature reversed that: the metalloid now sets the root name and the dominant divalent metal sets a suffix in brackets.
The consequence for a collection is blunt. Counting the September 2026 IMA-CNMNC Master List, the group holds 34 valid species: seven tetrahedrites, eight tennantites, four argentotetrahedrites, two argentotennantites, three goldfieldites, four hakites, and the keno- and rozhdestvenskayaite names. The three bare names a collector's labels actually carry — tetrahedrite, tennantite, freibergite — are on none of them.
Two of the seven, tetrahedrite-(Fe) and tetrahedrite-(Zn), are marked Rd, redefined, with the year given as 2019 s.p. They are not new minerals. They are the old tetrahedrite, split.
This site takes the same position it takes on apophyllite, heulandite and stilbite: the page is filed under the name on the label, and the page says what the label now means. Renaming the page would make it unfindable by the people holding the specimens.
What you can determine, and what needs a microprobe
Determinable in the hand: that it is a tetrahedrite-group mineral. Tetrahedral crystals to 15 cm, metallic and commonly splendent lustre, flint-grey to iron-black colour, a black to brown streak, hardness 3 to 4.5, and contact or penetration twins on {111} that are commonly repeated. No cleavage is recorded at all; the fracture is subconchoidal.
Determinable with care: which end of the antimony-arsenic series you are nearer, from density. The Handbook of Mineralogy gives 4.97 for tetrahedrite and 4.62 for tennantite, a 7.6% difference, which a careful specific gravity measurement at home can resolve on a clean, void-free piece. Colour helps at the extremes: high-arsenic, low-iron tennantite runs towards cherry-red in transmitted light on thin edges.
Not determinable without instruments: the suffix. Whether a grey tetrahedral crystal is tetrahedrite-(Fe) or tetrahedrite-(Zn) is a question about which divalent cation dominates one site, and the answer comes from an electron microprobe. A dealer who prints a suffix without an analysis is guessing, and so is a collector who writes one on a label. The honest label reads tetrahedrite group, with the locality and the date.
Localities, and the Cornish connection
The Handbook calls tetrahedrite one of the most common of the sulfosalts and then notes that only a few localities have produced well-crystallised material. Those named are Freiberg in Saxony and Clausthal and Horhausen in the Harz; Brixlegg in the Tirol; Botés and Cavnic in Romania; Irazein in Ariège, France, for a few exceptionally large crystals; Sainte-Marie-aux-Mines; and the Herodsfoot mine in Cornwall.
Herodsfoot, near Liskeard, is the British entry on the sheet and it is a serious one: the mine is known for tetrahedrite with bournonite, and for the classic Cornish cogwheel bournonite alongside it. The wider context for Cornwall and for bournonite is on their own pages.
The Handbook's association list is the standard base-metal vein suite: chalcopyrite, galena, sphalerite, pyrite, bornite, acanthite, calcite, dolomite, siderite, baryte, fluorite and quartz. Tetrahedrite-group minerals are a silver ore wherever silver substitutes into them, which is what made freibergite an economic term long before it was a mineralogical one.
The rest of this reference section is indexed at the species index. Nothing on this site is for sale and there is no catalogue; the wanted list is the only commercial route, and Herodsfoot material with an old label is on it.