Stannite
Stannite is Cu2FeSnS4, a steel-grey tin sulphide: tetragonal, hardness 4, density 4.3 to 4.5, type locality Wheal Rock, Cornwall. How it differs from kësterite.
Stannite is a copper iron tin sulphide, Cu2FeSnS4: tetragonal, steel-grey to iron-black, hardness 4, density 4.3 to 4.5, with a blackish streak and metallic lustre. Its Handbook sheet marks Wheal Rock, near St Agnes, Cornwall, as the type locality. Worked, it is 27.61% tin by mass; zinc-dominant material of the same build is kësterite.
In short
- The identity card, from the Handbook of Mineralogy sheet: Cu2FeSnS4, tetragonal, steel-grey to iron-black, may tarnish blue, streak blackish, metallic, hardness 4, measured density 4.3 to 4.5. The September 2026 IMA-CNMNC Master List agrees on the formula: status G, 1832, United Kingdom.
- Five rows, one pattern. A regex over the IMA list for formulas of the form Cu2-M-SnS4 returns five: stannite and ferrokësterite (Fe), kësterite (Zn), černýite (Cd) and velikite (Hg). The metal in the M position names the species, except that stannite and ferrokësterite share iron.
- The iron-or-zinc line, worked on the sheets’ own analyses. Iron is 99.5% of iron plus zinc in the Chocaya analysis and 85.7% at Oruro: stannite. It is 15.4% at the Kester deposit and 26.1% at St. Michael’s Mount: kesterite.
- The documented negative: ferrokësterite. It has the same IMA formula as stannite, Cu2FeSnS4, the same calculated density, 4.490, and an iron-dominant analysis, 67.0%. Chemistry and the scale cannot separate the two; the structure does, point group -42m against -4. Its type locality is the Cligga mine, Cornwall.
- A minor tin source beside cassiterite. Stannite is 27.61% tin; cassiterite, SnO2, is 78.77%, and its sheet calls it the principal ore of tin. The stannite sheet says that in Cornwall stannite may constitute an ore mineral.
| Mineral | IMA formula | IMA status, year, country | Point group (rendered sheet) | Hardness | Density | Colour | Streak | Fe share of Fe + Zn in the sheet's analysis | Tin by mass (worked) |
|---|---|---|---|---|---|---|---|---|---|
| Stannite | Cu2FeSnS4 | G; 1832; United Kingdom | -42m | 4 | 4.3 to 4.5 measured | Steel-grey to iron-black | Blackish | 99.5% (Chocaya); 85.7% (Oruro) | 27.61% |
| Ferrokësterite | Cu2FeSnS4 | Rn; 1985-012; United Kingdom | -4 | About 4 | Not determined; 4.490 calculated | Steel-grey | Black | 67.0% (Cligga mine) | 27.61% |
| Kësterite | Cu2ZnSnS4 | G; 1956; Russia | -4 | 4.5 | 4.54 to 4.59 measured | Greenish black | Black | 15.4% (Kester); 26.1% (St. Michael's Mount) | 27.02% |
| Cassiterite | SnO2 | G; 1832; United Kingdom | 4/m 2/m 2/m | 6 to 7 | 6.98 to 7.01 measured | Black, brownish black, reddish brown, red, yellow, grey, white | White, pale brown, pale grey | Not applicable | 78.77% |
What is stannite? Copper, iron and tin in one sulphide
Cu2FeSnS4, and both sources agree. The Handbook of Mineralogy sheet and the September 2026 IMA-CNMNC Master List print the same formula; the IMA row gives status G, 1832, United Kingdom. Worked on standard atomic weights, the formula mass is 429.89: copper 29.56%, iron 12.99%, tin 27.61%, sulphur 29.83%. The sheet’s ideal column prints 29.58, 12.99, 27.61 and 29.82.
The name is from the Latin stannum, tin. The sheet files it in the stannite group, dimorphous with ferrokesterite, and in polished section gray with olive-green tinge, with distinct violet and slate-green anisotropism.
Habit. Rarely as crystals, to 6 cm, with a pseudo-octahedral habit due to twinning; also massive, granular, and disseminated. The twins are penetration twins on {102}, with [112] as twin axis and {112} as composition plane, read from the rendered sheet. Twin laws in general are on mineral twinning explained.
Stannite or kësterite? The iron-or-zinc line
The rule: name the specimen for the dominant metal in the M position. Method: we searched the September 2026 IMA list by regex for formulas of the form Cu2, one metal, SnS4. Five rows match: stannite, Cu2FeSnS4; ferrokësterite, Cu2FeSnS4; kësterite, Cu2ZnSnS4, G, 1956, Russia; černýite, Cu2CdSnS4, A, 1976-057, Canada; and velikite, Cu2HgSnS4, A, 1996-052, Kyrgyzstan. The Handbook spells kësterite without the diaeresis and writes its formula Cu2(Zn,Fe)SnS4.
Worked on the sheets’ own analyses, iron as a share of iron plus zinc:
- Chocaya, Bolivia (stannite sheet): Fe 13.95, Zn 0.08 by mass. Iron 99.5%: stannite.
- Oruro, Bolivia (stannite sheet): Fe0.84 Zn0.14. Iron 85.7%: stannite, zinc-bearing.
- St. Michael’s Mount, Cornwall (kesterite sheet): Zn0.68 Fe0.24. Iron 26.1%: kësterite.
- Kester deposit, Russia (kesterite sheet): Zn0.77 Fe0.14. Iron 15.4%: kësterite.
In the hand the kesterite sheet gives greenish black, hardness 4.5 and density 4.54 to 4.59, against stannite’s steel-grey, 4 and 4.3 to 4.5. Those ranges nearly touch, and kesterite is recorded only as massive. A grey tin sulphide with no analysis should stay labelled as stannite or kësterite; the form is on how to label and catalogue a mineral collection.
Stannite and ferrokësterite: same formula, different structure
The documented negative. Ferrokësterite has the same IMA formula as stannite, Cu2FeSnS4, status Rn, IMA 1985-012, United Kingdom. Its sheet gives the same calculated density, 4.490, and its Cligga mine analysis, Fe0.67 Zn0.33, is iron-dominant at 67.0%. The iron-or-zinc line therefore cannot separate it from stannite, and nor can a balance.
What does separate them is the structure. The rendered sheets give stannite point group -42m and ferrokësterite -4, the same as kësterite; the ferrokesterite sheet gives its space group by analogy to kesterite. That is an X-ray question. The ferrokesterite sheet describes it as massive, granular, to 0.5 mm, and records no crystals.
Why it matters for a Cornish label. The ferrokesterite sheet marks the Cligga mine, Perranzabuloe, Cornwall, as its type locality, and the kesterite sheet lists the Cligga mine and St. Michael’s Mount. A grey tin sulphide from those mines labelled stannite may be any of the three. The term type locality is explained on what is a type locality.
Where stannite is found: Wheal Rock, Bolivia and Hunan
Cornwall first. The Distribution field opens In Cornwall, England, from Wheal Rock, near St. Agnes [TL], and at a number of other mines, where it may constitute an ore mineral. It names no other Cornish mine, and we add none. See Cornwall.
Elsewhere it lists Cínovec (Zinnwald), Czech Republic; Broken Hill, New South Wales, and Zeehan, Tasmania; in Bolivia, the Itos and San José mines, Oruro, Llallagua, Chocaya, Cerro Rico and Uncia; the Peerless and Etta mines near Keystone, South Dakota; the Brunswick tin mines, New Brunswick; and large crystals from the Yaogangxian mine, Hunan Province, China.
How it forms and with what. The Occurrence field reads in tin-bearing vein deposits of hydrothermal origin. The associates are chalcopyrite, sphalerite, tetrahedrite, arsenopyrite, pyrite, cassiterite and wolframite. Telling stannite from cassiterite, its commonest tin companion, is on stannite or cassiterite. The rest of 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.