Pentlandite
Pentlandite, (Ni,Fe)9S8, is pale bronze-yellow: cubic, hardness 3.5 to 4, density 4.6 to 5.0, streak pale bronze-brown. Nickel: 28.1 to 50.7% of metal atoms.
Pentlandite is iron nickel sulfide, (Ni,Fe)9S8 on the IMA list (G, 1856, United Kingdom): cubic, massive and granular, pale bronze-yellow, hardness 3.5 to 4, density 4.6 to 5.0. USGS names it the principal ore mineral of magmatic sulfide nickel deposits and calls it ferromagnetic, though its Handbook sheet prints no magnetic property.
In short
- The species. The Handbook of Mineralogy sheet gives (Fe,Ni)9S8, cubic, Fm−3m, massive and granular, rarely in crystals to 10 cm embedded in other sulfides; parting on {111}, hardness 3.5 to 4, density 4.6 to 5.0, pale bronze-yellow, streak pale bronze-brown. The September 2026 IMA-CNMNC Master List writes it (Ni,Fe)9S8, nickel first, status G, 1856, United Kingdom; the sheet marks Craignure, Scotland, as type locality.
- The iron–nickel split. Converted to atoms per 8 sulfur, the sheet’s three analyses give Worthington mine, Sudbury, Ni 4.60, Fe 4.30, Co 0.17; Mount Colin, Australia, Ni 4.15, Fe 3.63, Co 1.48; Mount Dun, New Zealand, Fe 5.89, Ni 2.51, Co 0.53. Nickel holds 50.7%, 44.9% and 28.1% of the metal atoms. Two are nickel-dominant, one iron-dominant.
- One formula, two species. A field scan of the IMA list, checked by a token scan, finds 2 rows written exactly (Ni,Fe)9S8: pentlandite and godlevskite (A, 1968-032, Russia). The godlevskite sheet gives orthorhombic, pseudotetragonal, grains to 1 mm. The same scans find 7 rows ending 9S8 or )8S8, three of them named for pentlandite: pentlandite, cobaltpentlandite (Co9S8) and argentopentlandite (Ag(Fe,Ni)8S8).
- Nickel ore and magnet, by USGS. The USGS National Minerals Information Center nickel page says the bulk of mined nickel comes from laterites or from magmatic sulfide deposits where the principal ore mineral is pentlandite. USGS OFR 99-529 pulled 2 samples at a best 0.01 amp and names it ferromagnetic; the sheet prints no magnetic property. That gap is the subject of is pentlandite magnetic.
- Documented failure: pyrrhotite. The sheet says pentlandite is commonly intimately associated with pyrrhotite. A 20.00 g piece reads 15.65 to 16.00 g in water as pentlandite and 15.63 to 15.70 g as pyrrhotite, overlapping from 15.65 to 15.70; hardness 3.5 to 4 sits inside pyrrhotite’s 3.5 to 4.5. The streak separates them: pale bronze-brown against dark grayish black.
| Name | Formula (IMA), status | System (sheet) | Hardness | Density | 20.00 g piece in water | Streak (sheet) | Colour (sheet) | Magnetism (sheet) |
|---|---|---|---|---|---|---|---|---|
| Pentlandite | (Ni,Fe)9S8; G, 1856 | Cubic | 3.5–4 | 4.6–5.0 | 15.65–16.00 g | Pale bronze-brown | Pale bronze-yellow | None printed |
| Godlevskite | (Ni,Fe)9S8; A, 1968-032 | Orthorhombic, pseudotetragonal | n.d. | 5.273 calc. | 16.21 g (calc.) | n.p. | Pale yellow in polished section | None printed |
| Cobaltpentlandite | Co9S8; Rn, 1962 s.p. | Cubic | n.d. | 5.22 calc. | 16.17 g (calc.) | n.p. | Slightly lighter bronze-yellow than pentlandite, in polished section | None printed |
| Argentopentlandite | Ag(Fe,Ni)8S8; A, 1970-047 | Cubic | n.d. | 4.66 calc. | 15.71 g (calc.) | n.p. | Bronze-brown | None printed |
| Pyrrhotite | Fe7S8; G, 1835 | Monoclinic, pseudohexagonal | 3.5–4.5 | 4.58–4.65 | 15.63–15.70 g | Dark grayish black | Bronze-yellow to pinchbeck-brown | Magnetic, varying inversely with iron content |
| Millerite | NiS; G, 1845 | Hexagonal | 3–3.5 | 5.5 | 16.36 g | Greenish black | Pale brass-yellow to bronze-yellow | None printed |
| Chalcopyrite | CuFeS2; G, 1725 ? | Tetragonal | 3.5–4 | 4.1–4.3 | 15.12–15.35 g | Greenish black | Brass-yellow | None printed |
| Cubanite | CuFe2S3; G, 1843 | Orthorhombic | 3.5 | 4.03–4.18 | 15.04–15.22 g | n.p. | Brass-yellow to bronze-yellow | Strongly magnetic |
What is pentlandite? The iron nickel sulfide of nickel ores
Pentlandite is (Ni,Fe)9S8, a pale bronze-yellow cubic sulfide that is almost always massive. The Handbook of Mineralogy pentlandite sheet gives point group 4/m −3 2/m, space group Fm−3m, massive, commonly in granular aggregates; rarely in crystals, to 10 cm, embedded in other sulfides. It parts on {111}, fractures conchoidally and is brittle; hardness 3.5 to 4, Vickers 268 to 285, measured density 4.6 to 5.0 against a calculated 4.956. Pale bronze-yellow, reddish brown when argentian; streak pale bronze-brown; lustre metallic.
Two ways of writing one formula. The Handbook heads the sheet (Fe,Ni)9S8; the September 2026 IMA list writes (Ni,Fe)9S8, status G, 1856, with the United Kingdom as country of first description, which agrees with the sheet’s Craignure, near Inverary, Strathclyde, Scotland [TL]. The sheet places it in the pentlandite group and says it forms a series with cobalt pentlandite. It is named for Joseph Barclay Pentland (1797–1873), Irish natural scientist and historian, who first noted the mineral; the type material is at The Natural History Museum, London.
Occurrence. The sheet: commonly intimately associated with pyrrhotite; in ultramafic rocks and perhaps derived from them by magmatic segregation; also in mantle xenoliths and undersea black smoker deposits; rarely in meteorites. Its associates are pyrrhotite, troilite, chalcopyrite, cubanite, mackinawite and magnetite. The USGS National Minerals Information Center nickel page says the bulk of the nickel mined comes from laterites, or from magmatic sulfide deposits where the principal ore mineral is pentlandite.
How much nickel is in pentlandite? The iron–nickel split
There is no single figure: the sheet’s three analyses put nickel at 50.7%, 44.9% and 28.1% of the metal atoms. Method: divide each weight percent by the standard atomic weight (Fe 55.845, Ni 58.693, Co 58.933, S 32.06) and scale to 8 sulfur. Worthington mine, Sudbury, Canada (34.48 wt% Ni, 30.68 Fe, 1.28 Co, 32.74 S): Ni 4.60, Fe 4.30, Co 0.17, metals 9.08. Mount Colin, Australia (30.8 Ni, 25.6 Fe, 11.0 Co, 32.4 S): Ni 4.15, Fe 3.63, Co 1.48, metals 9.26. Mount Dun area, New Zealand (19.3 Ni, 43.1 Fe, 4.1 Co, 33.6 S): Fe 5.89, Ni 2.51, Co 0.53, metals 8.93. The sheet prints Ni 4.16 and a sum of 9.27 for Mount Colin and 9.07 for Worthington; the 0.01 differences are rounding.
What the split shows. Two analyses are nickel-dominant and one iron-dominant, all printed on the one sheet as pentlandite. Cobalt reaches 16.0% of the metals at Mount Colin; the sheet says pentlandite forms a series with cobalt pentlandite. For a reference point only, the half-and-half composition Fe4.5Ni4.5S8 is 34.22% nickel by mass; the analyses run from 19.3 to 34.48 wt%. This page does not reclassify any of the three analyses.
One formula, two species. A field scan of the IMA list, splitting each line on runs of two or more spaces and checked by a token scan, finds 2 rows written exactly (Ni,Fe)9S8: pentlandite and godlevskite, approved 1968 from Russia. The godlevskite sheet gives orthorhombic, pseudotetragonal grains to 1 mm, with no measured density. A formula does not name the species; the structure does. The nickel sulfide with a fixed formula, NiS, is millerite, with its nickel worked on its own page.
Pentlandite or pyrrhotite? Weight fails, streak works
The streak separates pentlandite from pyrrhotite; weight and hardness do not. At the sheets’ measured densities a 20.00 g piece reads 15.65 to 16.00 g in water as pentlandite and 15.63 to 15.70 g as pyrrhotite, a shared band from 15.65 to 15.70 g. Pentlandite’s hardness, 3.5 to 4, lies inside pyrrhotite’s 3.5 to 4.5. The pentlandite sheet gives a pale bronze-brown streak; the pyrrhotite sheet dark grayish black. The methods are on how to use a streak plate and how to measure specific gravity at home.
The other brass-coloured sulfides. chalcopyrite reads 15.12 to 15.35 g and has a greenish black streak; cubanite, whose sheet says it occurs in pyrrhotite–pentlandite ores intergrown with chalcopyrite, reads 15.04 to 15.22 g. Millerite reads 16.36 g and grows in capillary needles; pyrite is hardness 6 to 6.5. The pentlandite sheet calls it commonly intimately associated with pyrrhotite, and the cubanite sheet describes intimate oriented intergrowths with chalcopyrite, so a weighed piece may be a weighed mixture.
The magnet does not settle it either. The pyrrhotite sheet says magnetic and the cubanite sheet strongly magnetic; USGS names pentlandite ferromagnetic as well. A pull from a bronze sulfide therefore does not pick out one of them. What each source records is on is pentlandite magnetic and is pyrrhotite magnetic.
Where pentlandite is found
The Distribution field says pentlandite occurs at many localities. Craignure, near Inverary, Strathclyde, Scotland [TL]; Wheals Jane and Falmouth, Kea, Cornwall; Espedalen, near Lillehammar, Opland, Norway; Outokumpu, Vuonos, Miihkali and Hietajärvi in east Finland, the Hitura nickel deposit in west Finland and Rarrua in the north; the Rustenburg district, in the Merensky Reef, Bushveld complex, South Africa; the Mount Dun area, Nelson Province, New Zealand; Lime Creek and Mount Colin, Queensland; Coolgardie and Kambalda, Western Australia; the Lord Brassey mine, Heazlewood, Tasmania; the Kamishi mine, Iwate Prefecture, Japan; a number of mines at Sudbury, Ontario; and the Voisey’s Bay Ni–Cu–Co deposit, Labrador.
Its neighbours. The platinum arsenide of the same Ni–Cu ores is sperrylite; the copper-red nickel arsenide is nickeline. Pentlandite is not an arsenic mineral, and nothing on this page is health or safety 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.