Jamesonite
Jamesonite is Pb4FeSb6S14, a gray-black sulfosalt in needles and felted masses, hardness 2.5, density 5.63, type locality Cornwall. What its iron atom does.
Jamesonite is lead iron antimony sulfide, Pb4FeSb6S14 on the September 2026 IMA list: a monoclinic sulfosalt in gray-black needles and feltlike masses, hardness 2.5, density 5.63, type locality around St. Endellion, Cornwall. Worked, it is 40.15% lead and 2.71% iron; the one iron atom is what separates it from robinsonite, Pb4Sb6S13.
In short
- The species. The Handbook of Mineralogy sheet gives monoclinic crystals elongated along [001], acicular and fibrous to 10 cm, also feltlike, columnar, radial and plumose masses; hardness 2.5, density 5.63, gray-black and metallic, cleavage good on {001}. The September 2026 IMA-CNMNC Master List writes Pb4FeSb6S14, status G, 1825, United Kingdom.
- The iron ledger. By formula arithmetic, Pb4FeSb6S14 is robinsonite, Pb4Sb6S13, plus FeS. A script over the IMA list finds 2 rows of the jamesonite pattern, iron in jamesonite and manganese in benavidesite. The sheet’s two analyses work out at 0.99 and 0.91 iron atoms per 11 metal atoms, against 1 in the formula.
- Documented failure: weight. A 20.00 g piece reads 16.45 g in water as jamesonite and 16.45 to 16.52 g as robinsonite; plagionite reads 16.39 g. The balance cannot separate them. It does separate boulangerite, at 16.77 g, 0.33 g heavier, and stibnite, at 15.68 g.
- Where it is found. The sheet says numerous localities, only a few with rich material: Cornwall around St. Endellion [TL] and St. Kew; Freiberg and the Harz, Germany; Příbram; Baia Sprie and Herja, Romania; Trepča, Serbia; Sala, Sweden; Oruro, Bolivia; Zacatecas, Mexico; Slate Creek, Idaho; and Dachang, China.
| Composition | Source | Pb (wt%) | Fe or Mn (wt%) | Sb (wt%) | S (wt%) | Fe or Mn per 11 metal atoms | Density; 20.00 g in water |
|---|---|---|---|---|---|---|---|
| Jamesonite, ideal Pb4FeSb6S14 | IMA (G, 1825, United Kingdom); sheet column (3) | 40.15 | Fe 2.71 | 35.39 | 21.75 | Fe 1.00 | 5.63; 16.45 g |
| Jamesonite, Cornwall, average of three | Sheet analysis (1) | 40.14 | Fe 2.64 (Cu 0.18) | 34.25 | 22.34 | Fe 0.99 (Cu 0.06) | As above |
| Jamesonite, Tresungers mine, St. Endellion | Sheet analysis (2), electron microprobe | 42.2 | Fe 2.5 | 35.3 | 20.5 | Fe 0.91 | As above |
| Benavidesite, ideal Pb4MnSb6S14 | IMA (Rn, 1980-073, Peru); series with jamesonite (both sheets) | 40.17 | Mn 2.66 | 35.41 | 21.76 | Mn 1.00 | n.d. |
| Robinsonite, ideal Pb4Sb6S13 | IMA (G, 1952, USA) | 41.94 | — | 36.97 | 21.09 | 0 | 5.64–5.75; 16.45–16.52 g |
| Parajamesonite, Pb4FeSb6S14 | Sheet only; no IMA line; dimorph of jamesonite (sheet) | As jamesonite | Fe 2.71 | As jamesonite | As jamesonite | 1.00 | 5.482; 16.35 g |
What is jamesonite? A lead–iron–antimony sulfosalt first described from Cornwall
Jamesonite is Pb4FeSb6S14, a gray-black, metallic lead sulfosalt that grows as needles, fibres and felted masses. The Handbook of Mineralogy jamesonite sheet gives monoclinic crystals, point group 2/m, elongated and striated along [001], acicular and fibrous, to 10 cm, rarely in rings and spheres; also feltlike masses, massive, columnar, radial and plumose. Twinning is on {100}, with lamellae very commonly seen in polished section. Cleavage is good on {001} and reported on {010} and {120}; it is brittle, hardness 2.5, density 5.63 measured against 5.76 calculated. It is gray-black, may tarnish iridescent, and the sheet prints no streak.
What the IMA list records. Jamesonite, Pb4FeSb6S14, status G (grandfathered), 1825, United Kingdom. The sheet marks St. Endellion, Cornwall, as the type locality and names the mineral for Robert Jameson (1774–1854), the Scottish mineralogist of Edinburgh who first described it; more on the term at what a type locality is. The sheet places it among lead sulfosalts: its Association line opens “Other lead sulfosalts”. The sulfosalt question for a copper mineral is worked on is enargite a sulfosalt.
Where it forms. Typically a late-stage hydrothermal mineral in Pb–Ag–Zn veins formed at low to medium temperatures, with other lead sulfosalts, pyrite, sphalerite, galena, tetrahedrite, stibnite, quartz, siderite, calcite, dolomite and rhodochrosite.
What makes jamesonite jamesonite? The iron ledger
The iron ledger: jamesonite is the 2:3 lead–antimony sulfide that carries one iron atom; take the iron away and the formula is robinsonite’s. Pb4FeSb6S14 minus FeS is Pb4Sb6S13, the IMA formula of robinsonite, and the formula masses agree to the third decimal, 2064.045. A field scan of the September 2026 IMA list for formulas written Pb4, any one other element, Sb6S14, checked by a whole-line token scan, finds 2: jamesonite with iron and benavidesite, Pb4MnSb6S14 (Rn, 1980-073, Peru), with manganese. The benavidesite sheet says it forms a series with jamesonite, and the jamesonite sheet says the same.
Worked on the sheet’s analyses. Divide each weight percentage by its atomic weight and scale to 11 metal atoms. The Cornwall average gives Pb 4.06, Fe 0.99, Cu 0.06, Sb 5.89; the Tresungers mine microprobe analysis, from St. Endellion, gives Pb 4.16, Fe 0.91, Sb 5.92. Both sit close to one iron atom. Ideal jamesonite is 2.71% iron; the analyses print 2.64% and 2.5%.
What the ledger cannot do. Iron at 2.71% is not something the eye or a balance can read; telling jamesonite from robinsonite or benavidesite takes an analysis. The parajamesonite sheet gives the same formula, Pb4FeSb6S14, as a dimorph, but the September 2026 IMA list has no line containing the name, so this page names it only as the sheet does.
Jamesonite or boulangerite? What the two sheets print
Jamesonite and boulangerite are both lead-gray to gray-black antimony sulfosalt needles; the sheets separate them on weight, crystal length and streak, not on hardness. The boulangerite sheet gives needlelike crystals to 1 cm, a brownish streak and density about 6.2; jamesonite’s gives crystals to 10 cm, no printed streak and density 5.63. A 20.00 g piece reads 16.45 g in water as jamesonite and 16.77 g as boulangerite, 0.33 g apart. Hardness overlaps: 2.5 against 2.5 to 3. Cleavage is on different forms, {001} good on jamesonite and {100} distinct on boulangerite. Methods: how to measure specific gravity at home and how to use a streak plate.
Documented failure: the neighbours a balance cannot split. Robinsonite reads 16.45 to 16.52 g, the same as jamesonite at the low end; plagionite reads 16.39 g, 0.06 g away; parajamesonite 16.35 g. bournonite, at 16.57 g, is 0.12 g away, and its sheet records twins on {110} commonly forming cross or cogwheel aggregates. stibnite, Sb2S3, at density 4.63, reads 15.68 g, and its sheet calls it highly flexible, where jamesonite’s says brittle. Stibnite’s magnetism question is on is stibnite magnetic.
Old labels. The jamesonite sheet calls some habits plumose. The IMA list has a separate row named plumosite, Pb2Sb2S5, status Q, questionable, 1845, Germany; no source fetched for this page says what an old plumosite label held, so this page does not translate it.
Where is jamesonite found? Cornwall, Mexico and the Andes
The jamesonite sheet’s Distribution field says numerous localities, only a few with rich material. It names Cornwall around St. Endellion [TL] and St. Kew; Freiberg, Saxony, and Magdesprung, the Selke Valley and Clausthal in the Harz; Příbram, Czech Republic; Aranyidka, and Baia Sprie (Felsőbánya) and Herja (Kisbánya) in the Baia Mare district, Romania; Trepča, Serbia; Sala, Västmanland, Sweden; Machacamarca, Poopó, and Huanuni, Oruro, Bolivia; in Mexico, the Noche Buena mine near Mazapil, the Santa Rita mine at Nieves, and relatively thick crystals from the Noria mine near Sombrerete, Zacatecas; Slate Creek, Shoshone Co., Idaho; and the Dachang district, Guangxi, China.
What grows with it. The Association line names quartz, calcite, dolomite, siderite and rhodochrosite as well as sulfides; it does not name fluorite. Whether a given needle inside quartz or fluorite is jamesonite is not something the sheets settle. No USGS or BGS text was fetched, so this page makes no ore or use claim. Jamesonite is 40.15% lead and 35.39% antimony by mass; see toxic minerals in a collection, and nothing here is health advice. The rest is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.