Stephanite
Stephanite, Ag5SbS4: orthorhombic iron-black silver antimony sulphosalt, hardness 2 to 2.5, density 6.26, 68.33% silver, type locality Freiberg, Saxony.
Stephanite is a silver antimony sulphosalt, Ag5SbS4 on the IMA list (G, 1845): orthorhombic iron-black crystals to 6 cm, often twinned into pseudohexagonal groups, hardness 2 to 2.5, density 6.26, streak iron-black. It is 68.33% silver by mass, and the USGS lists it among the principal silver minerals. Its type locality is Freiberg, Saxony.
In short
- The five-to-one check. The September 2026 IMA-CNMNC Master List and the Handbook of Mineralogy sheet both write Ag5SbS4: five silver per antimony. Worked in atoms, the sheet’s Copiapó, Chile, analysis gives 5.09 and its Cornwall analysis 4.85. On standard atomic weights the formula is 68.33% silver, 15.43% antimony and 16.25% sulphur.
- The Ag-per-Sb ladder. A script over the IMA list finds 8 rows written in silver, antimony and sulphur alone. Silver per antimony runs 1 (miargyrite, cuboargyrite, baumstarkite), 3 (pyrargyrite, pyrostilpnite, pyradoketosite), 5 (stephanite) and 8 (argentopolybasite). Stephanite is the only row at 5.
- Is stephanite an ore? The USGS Open-File Report 2004-1251, Mineral Commodity Profiles: Silver lists stephanite, Ag5SbS4, in its Table 3 of principal silver minerals, taken from Heyl and others (1973). Documented failure: the same table prints proustite as (Ag,Cu)16Sb2S11 and polybasite as Ag3AsA3, one row out of step. Take the formula from the IMA list, not from a commodity table.
- Telling the black silver minerals apart. polybasite, acanthite and stephanite all streak black; proustite and pyrargyrite streak red, on how to use a streak plate. Acanthite is sectile where stephanite is brittle. Why the balance cannot separate polybasite from stephanite is worked on the polybasite page and is not repeated here.
- Antimony and silver sulphide dust. Stephanite carries 15.43% antimony by mass. The general position is on toxic minerals in a collection; this page is not safety or health advice.
| Species or analysis | IMA formula | Status, year | Ag per Sb | Ag by mass | Note |
|---|---|---|---|---|---|
| Miargyrite | AgSbS2 | G, 1829 | 1 | 36.72% | Same formula as cuboargyrite |
| Cuboargyrite | AgSbS2 | A, 1997-004 | 1 | 36.72% | — |
| Baumstarkite | Ag3Sb3S6 | A, 1999-049 | 1 | 36.72% | Same ratio, written ×3 |
| Pyrargyrite | Ag3SbS3 | G, 1831 | 3 | 59.76% | Purplish red streak on its sheet |
| Pyrostilpnite | Ag3SbS3 | G, 1868 | 3 | 59.76% | Dimorphous with pyrargyrite (pyrargyrite sheet) |
| Pyradoketosite | Ag3SbS3 | A, 2019-132 | 3 | 59.76% | — |
| Stephanite | Ag5SbS4 | G, 1845 | 5 | 68.33% | Iron-black streak |
| Stephanite, Copiapó, Chile | Analysis (1) | — | 5.09 | 68.65% (printed) | Traces of As and Cu |
| Stephanite, Cornwall, England | Analysis (2) | — | 4.85 | 68.21% (printed) | Trace of Fe |
| Argentopolybasite | [Ag9AgS4][Ag6Sb2S7] | A, 2021-119 | 8 | 74.33% | Bracketed formula as the IMA list writes it |
What is stephanite? A silver antimony sulphosalt
Stephanite is Ag5SbS4 on the September 2026 IMA list, status G, 1845, country Germany. The Handbook of Mineralogy stephanite sheet prints the same formula and names it in honour of the Archduke Victor Stephan (1817–1867), former Mining Director of Austria. Its occurrence line reads a late-stage mineral in hydrothermal silver deposits, and its associates are proustite, acanthite, silver, tetrahedrite, galena, sphalerite and pyrite.
On the sheet. Orthorhombic, point group mm2, space group Cmc21, in short prismatic to tabular crystals to 6 cm, also elongated along [100], with {110} striated parallel to [1-14]; massive, compact and disseminated. Twinning on {110} is commonly repeated to form pseudohexagonal groups. Cleavage imperfect on {010} and {021}, fracture subconchoidal, brittle. Hardness 2 to 2.5; density 6.26 measured and 6.28 to 6.32 calculated. Iron-black, pale grey in polished section, with an iron-black streak and a metallic lustre. The indices were read from the rendered sheet, because the text layer drops overbars.
Its chemistry, worked. On standard atomic weights Ag5SbS4 has a formula mass of 789.34 and is 68.33% silver, 15.43% antimony and 16.25% sulphur. The sheet’s ideal column prints 68.33, 15.42 and 16.25, which is the method’s positive control.
Why is five silver per antimony the useful number?
Because the analyses agree on it. Recast to atoms, the sheet’s Copiapó, Chile, analysis (Ag 68.65, Sb 15.22, S 16.02) gives 5.09 silver per antimony and 4.00 sulphur; the Cornwall analysis (Ag 68.21, Sb 15.86, S 15.95) gives 4.85 and 3.82. Each is within 0.15 of the formula’s 5.
The Ag-per-Sb ladder. By script over the IMA list, 8 rows are written in silver, antimony and sulphur alone. Their silver per antimony is 1, 3, 5 or 8, and stephanite holds 5 by itself. An analysis near 3 points to the pyrargyrite family, near 8 to argentopolybasite. Copper-bearing polybasite is not on this ladder; its As/Sb switch is set out on its own page. The silver sulphides without antimony are on acanthite.
Is stephanite a silver ore?
The USGS lists it as a principal silver mineral. The USGS Open-File Report 2004-1251, Mineral Commodity Profiles: Silver, by Butterman and Hilliard, reproduces in its Table 3 the principal silver minerals listed by Heyl and others (1973), and stephanite, Ag5SbS4, is among them, with pyrargyrite (printed Pyargyrite), polybasite, proustite and acanthite. This page makes no claim about any working mine or deposit.
A documented failure in the table. The report’s text says 33 principal silver minerals; a script counts 34 entries in Table 3, one of them Ag-bearing Pb-Mn oxides. The table also prints proustite as (Ag,Cu)16Sb2S11 and polybasite as Ag3AsA3: the compositions sit one row out of step. The IMA list gives proustite Ag3AsS3 and polybasite [Ag9CuS4][(Ag,Cu)6(Sb,As)2S7]. Whether native silver counts as a mineral is on is silver a mineral.
Where is stephanite found? Freiberg, Cornwall and the Comstock Lode
The Distribution field calls it from many silver mining localities, typically in small amounts, and only rarely in fine specimens. In Germany, Freiberg [TL], Schneeberg and Marienberg, Saxony, and exceptional crystals from St. Andreasberg, Harz Mountains. In Slovakia, Banská Hodruša and Banská Štiavnica; in the Czech Republic, Jáchymov, Příbram and Třebsko; fine twins from Monte Narba, Sardinia; in England, twinned crystals from Wheal Boys, St. Endellion, Cornwall. Also Espedalen, Norway; Azegour, Morocco; Altyn-Topkan, Tadjikistan.
The Americas and Australia. The Cobalt district, Ontario; United Keno Hill Mines and the Husky mine, Elsa, Yukon; the Comstock Lode, Virginia City, Nevada; large crystals from Arizpe, Sonora, and Guanajuato and Fresnillo, Mexico; Chañarcillo, Chile; Colquechaca, Bolivia; San Cristobal, Peru; and Broken Hill, New South Wales. Freiberg is the one place the sheet marks as type locality; the term is explained on what is a type locality.
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.