Stibnite
Stibnite is Sb2S3, 71.69% antimony: hardness 2, density 4.63, lead-grey and highly flexible, in crystals to 0.65 m. The main ore of antimony, from its sheet.
Stibnite is antimony sulphide, Sb2S3, the Handbook's most important ore of antimony: orthorhombic, hardness 2, density 4.63, lead-grey with a lead-grey streak and one perfect cleavage. It is 71.69% antimony by mass. Its crystals are recorded to 0.65 m, and it is the only one of 18 flexible sheets in this site's reference set called highly flexible.
In short
- Stibnite bends. The Handbook of Mineralogy records it as highly flexible but not elastic; slightly sectile, and bent crystals as not uncommon. Of the 176 sheets in this site's reference set, 18 record any flexibility, and stibnite's is the only entry with an intensifier.
- Its crystals are the second-longest of any sulphide in the set. Of the 25 sulphide and sulphosalt sheets that print a crystal size, only galena's to a meter beats stibnite's 0.65 m. Pyrrhotite is next at 40 cm.
- It is 71.69% antimony. Seven of the 176 sheets have antimony in the formula, and stibnite carries more than twice as much as any of the other six: bournonite 24.92%, pyrargyrite 22.48%, stephanite 15.43%.
- Tell it from galena by the weight and the cleavage. A 2 cm cube of stibnite weighs 37.0 g; galena's weighs 60.6 g. Stibnite has one perfect cleavage, where galena has three at right angles.
- The sheet records no magnetic property, which agrees with which minerals are magnetic. Whether its antimony matters to a collector is on toxic minerals in a collection, not here.
| Species | Formula | Hardness | Density | Cleavage | Tenacity | Largest crystal on the sheet | Sb by mass |
|---|---|---|---|---|---|---|---|
| Stibnite | Sb2S3 | 2 | 4.63 | Perfect and easy on {010} | Highly flexible but not elastic; slightly sectile | 0.65 m | 71.69% |
| Galena | PbS | 2.5 to 2.75 | 7.58 | Perfect on {001}: cubes | Brittle | To a metre on an edge | 0% |
| Bournonite | PbCuSbS3 | 2.5 to 3 | 5.83 | Imperfect | Brittle | 11 cm | 24.92% |
| Tetrahedrite | (Cu,Fe,Ag,Zn)12Sb4S13 | 3 to 4.5 | 4.97 | None recorded | Somewhat brittle | 15 cm | 29.23% |
| Molybdenite | MoS2 | 1 to 1.5 | 4.62 to 4.73 | Perfect, one plane | Lamellae flexible, not elastic | 15 cm | 0% |
| Pyrargyrite | Ag3SbS3 | 2.5 | 5.82 | Distinct | Brittle | 6 cm | 22.48% |
Is stibnite flexible? Yes: the only highly flexible sheet in the set
Stibnite's Handbook entry reads highly flexible but not elastic; slightly sectile. A bent stibnite blade stays bent: that is what not elastic means, and the sheet records bent crystals as not uncommon and twisted ones as rare.
Method. All 176 sheets in this site's reference set were converted with pdftotext -layout and searched case-insensitively for flexib, matching the letters fl or the stray glyph that replaces the fl ligature on the older sheets. 18 sheets record some flexibility; a literal search finds only 14. Positive controls: muscovite and talc, which print the ligature glyph, must match, and do. The same count is used on the ludlockite page.
Of the 18, stibnite's is the only entry with an intensifier. Most restrict flexibility to thin leaves, laminae or plates, as in molybdenite and muscovite. Stibnite's applies to the crystals. A long, thin, soft crystal that bends and does not spring back needs support along its length; the general approach is on handling and storage.
How big do stibnite crystals get? A ladder of 25 sulphide sheets
The Handbook records stibnite crystals to 0.65 m, slender to stout and complexly terminated, elongated along [001], and in radiating or confused groups of acicular crystals.
Method. The Crystal Data field was parsed from the 27 sheets whose header formula contains sulphur and no oxygen, which is how this page defines the sulphides and sulphosalts in the set. The largest size printed after to, as large as, as much as or up to was taken. 25 of the 27 print a size; marcasite and pararealgar do not. Orpiment's 60 cm is a cleavage across a foliated aggregate, so its crystal figure, 10 cm, is the one used.
The result: galena to a metre, then stibnite at 0.65 m, then pyrrhotite 40 cm, arsenopyrite and sphalerite 30 cm, pyrite and chalcocite 25 cm. Realgar is 12 cm and bournonite 11 cm. This is a count of what the sheets print, not a world record list: a sheet gives the size its authors chose to record.
What is stibnite made of? 71.69% antimony
On standard atomic weights, antimony 121.760 and sulphur 32.06, Sb2S3 has a formula mass of 339.70, and 243.52 / 339.70 = 71.69% antimony. The Handbook's ideal column prints Sb 71.69 and S 28.31. Its one real analysis, from Wolfsberg in the Harz, reads 71.45% antimony and 28.42% sulphur.
Against the rest of the set. A regular expression over the header formulas of the 176 sheets finds seven with antimony: stibnite, bournonite, pyrargyrite, pyrostilpnite, stephanite, tetrahedrite and freibergite. Calculated the same way, bournonite is 24.92% antimony, pyrargyrite and pyrostilpnite 22.48% and stephanite 15.43%. Tetrahedrite and freibergite are solid solutions; even their lightest end member, Fe12Sb4S13, would be only 30.94%. So stibnite has more than twice the antimony of any of the other six. Native antimony is not one of the 176 sheets and is not counted.
The Handbook calls stibnite dimorphous with metastibnite and says it forms a series with bismuthinite, Bi2S3. The September 2026 IMA-CNMNC Master List lists stibnite as grandfathered, 1832, country unknown; metastibnite 1888, USA; bismuthinite 1832. Neither of those two is in this site's reference set, so their properties are not given here. The Handbook derives the name from the Greek stibi, then Latin stibium, an old name for the mineral.
How to tell stibnite from galena
Both are lead-grey with a lead-grey streak and a metallic lustre, and stibnite's sheet names galena among its associates. Stibnite in turn is named in the Association field of four other sheets in the set: baryte, bournonite, orpiment and pararealgar, which forms from realgar in stibnite-bearing quartz veins. The streak test is on how to use a streak plate.
The quick rule: one cleavage and light means stibnite; three cleavages at right angles and heavy means galena. Stibnite's density is 4.63 against galena's 7.58, so a 2 cm cube, 8 cm³, weighs 37.0 g in stibnite and 60.6 g in galena. Stibnite breaks along one perfect and easy cleavage into blades; galena breaks into stepped cubes. Hardness 2 against 2.5 to 2.75 is too close to use. The weighing method is on how to measure specific gravity at home.
Stibnite's crystal shape is its own clue. Long striated prisms, often in radiating sprays, and sometimes visibly bent, are not a galena habit. Its sheet also records a tarnish: blackish or iridescent.
Where stibnite is found
The Handbook calls it of hydrothermal origin, formed in veins through a wide range of temperatures, with realgar, orpiment, cinnabar, galena, lead sulphantimonides, pyrite, marcasite, arsenopyrite, cervantite, stibiconite, calcite, ankerite, baryte and chalcedonic quartz. It describes stibnite as the most important ore of antimony, although large deposits are rare.
The sheet's list is of localities that have produced outstanding crystallised material. These are: the White Caps mine, Manhattan district, and the Murray mine, Elko County, Nevada; the San José and other mines at Oruro, Bolivia; Wolfsberg in the Harz and near Arnsberg in Germany; Kremnica and Banská Štiavnica in Slovakia; Příbram in the Czech Republic; and Baia Sprie and Herja in the Baia Mare district of Romania. It adds Massaic, Cantal and La Lucette, Mayenne in France; the Kusa mine near Bau, Sarawak; Thames, New Zealand; Bahar-Lou near Hamadan, Iran; and Kadamzhay, Kyrgyzstan. It singles out magnificent groups of crystals from the Ichinokawa mine near Saijo, Ehime Prefecture, Japan, and the Xikuangshan mine in Hunan, China, as economically very important. No British locality is recorded.
The rest of the sulphides are indexed at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.