Platinum
Native platinum, Pt: cubic, hardness 4 to 4.5, density 14 to 19, usually with iron. Over 80 atomic % Pt is native platinum; 20 to 50 % iron makes it ferroan.
Platinum is the native element Pt, an IMA species (G, 1748, Colombia): cubic, hardness 4 to 4.5, malleable, steel-gray, density 14 to 19 measured against 21.47 calculated. Natural grains carry iron, 5.3 to 16.5 wt% in the Handbook’s three analyses; the 1975 nomenclature calls 20 to 50 atomic % iron ferroan platinum.
In short
- The 80 percent line. Cabri and Feather’s 1975 nomenclature, approved by the IMA commission, defines native platinum as a face-centred cubic alloy with more than 80 atomic % Pt, counting minor Ir, Rh, Os and Pd with Pt and Cu or Ni with Fe. Ferroan platinum is a variety of native platinum with 20 to 50 atomic % Fe. If only a composition is known, the material is called Pt–Fe alloy.
- Worked on the sheet. The Handbook of Mineralogy platinum sheet prints three analyses as atomic proportions. Nizhni Tagil: 83.0% platinum-group atoms (Pt alone 79.0%), so native platinum. Chocó: 76.0%, with 24.0% Fe and Cu, so ferroan platinum. Birbir River: 60.0%, 40.0% Fe, ferroan platinum. All three need an X-ray pattern before the label can be more than Pt–Fe alloy.
- The Pt–Fe ladder. Three September 2026 IMA-CNMNC Master List rows are written in platinum and iron alone: isoferroplatinum Pt3Fe (91.29% Pt by mass), tetraferroplatinum PtFe (77.74%) and sidorovite PtFe3 (53.80%). Tulameenite, Pt2CuFe, is 76.57%. The sheets print platinum as nonmagnetic to distinctly magnetic when rich in iron, tetraferroplatinum as ferromagnetic and tulameenite as distinctly ferromagnetic.
- Documented failure: weight against gold. At 14 to 19 a 20.00 g piece of platinum reads 18.57 to 18.95 g in water; gold, at 19.3, reads 18.96 g, 0.01 g above platinum’s top. A balance separates platinum from native silver (18.02 to 18.20 g) but not from gold. The colour does: the gold sheet gives gold-yellow, the platinum sheet whitish steel-gray.
- Where. The Distribution field names the Pinto River, Chocó, Colombia [TL]; Platinum Creek, Goodnews Bay, Alaska; the Tulameen River district, British Columbia; a large district around Nizhni Tagil in the Urals and good crystals from the Konder massif, Sakha; and deposits along the Merensky Reef of the Bushveld complex.
| Name | Formula (IMA) | IMA status | Platinum by mass | Structure (sheet) | Density (sheet) | 20.00 g piece in water | Magnetism (sheet) |
|---|---|---|---|---|---|---|---|
| Platinum | Pt | G, 1748, Colombia | 100% (sheet analyses 79.48 to 92.2 wt% Pt) | Cubic, Fm3m | 14 to 19; calc. 21.472 | 18.57 to 18.95 g | Nonmagnetic to distinctly magnetic when rich in iron |
| Isoferroplatinum | Pt3Fe | A, 1974-012a, Canada | 91.29% | Cubic, Pm3m | n.d.; calc. 18.41 | 18.91 g (calc.) | Not printed |
| Tetraferroplatinum | PtFe | A, 1974-012b, South Africa | 77.74% | Tetragonal | n.d.; calc. [15.7] | 18.73 g (calc.) | Ferromagnetic |
| Tulameenite | Pt2CuFe | A, 1972-016, Canada | 76.57% | Tetragonal | 14.9 (synthetic); calc. 15.62 | 18.66 g (synthetic) | Distinctly ferromagnetic |
| Sidorovite | PtFe3 | A, 2022-056, Russia | 53.80% | No Handbook sheet (404) | No sheet | - | No sheet |
| Sperrylite | PtAs2 | G, 1889, Canada | 56.56% | Cubic, pyrite group | 10.58 | 18.11 g | Not printed |
| Cooperite | PtS; Handbook (Pt,Pd)S | Rd, 2022 s.p., South Africa | 85.89% | Tetragonal | 9.5 | 17.89 g | Not printed |
| Gold | Au | G | 0% | Cubic | 19.3 | 18.96 g | Not printed |
| Silver | Ag | G | 0% | Cubic | 10.1 to 11.1 | 18.02 to 18.20 g | Not printed |
What is platinum? The native metal
Native platinum is the element Pt crystallised in nature, usually with iron in it. The Handbook of Mineralogy platinum sheet gives cubic, point group 4/m −3 2/m, space group Fm3m, as cubic crystals, typically distorted, to 1.5 cm, commonly as grains or scales and rarely as nuggets or lumps up to 30 kg, twinned on {111} as interpenetrant contact twins. It is malleable and ductile with a hackly fracture, hardness 4 to 4.5, Vickers 297 to 339 at a 100 g load; whitish steel-gray to dark gray, white in polished section, metallic.
Density, as printed. The measured density is 14 to 19 and the calculated 21.472. The sheet does not give a reason for the gap, and this page does not supply one; the in-water figures below use the measured range. Its magnetism line reads nonmagnetic to distinctly magnetic when rich in iron.
What the IMA list records. The September 2026 list gives platinum, Pt, status G, 1748, with Colombia as the country of first description and a first reference to the Relacion Historica del Viage a la America Meridional (Madrid, 1748). The sheet marks the Pinto River, near Papayan, in the Department of Chocó, Cauca, Colombia, as the type locality and derives the name from the Spanish platina, diminutive of plata, silver. Whether native platinum counts as a mineral, and how it sits among the 39 IMA rows containing platinum, is answered on is platinum a mineral.
Is a platinum nugget pure platinum? The 80 percent line
Not usually: every analysis on the platinum sheet carries iron, from 5.3 to 16.50 wt%. Cabri and Feather 1975, Platinum–iron alloys: a nomenclature (Canadian Mineralogist 13, 117) set out the names for platinum–iron alloys, with the approval of the IMA commission. Native platinum is a disordered face-centred cubic alloy with more than 80 atomic % Pt. Ferroan platinum is a variety of native platinum, face-centred cubic, with 20 to 50 atomic % Fe. Isoferroplatinum is a primitive cubic species near Pt3Fe, and tetraferroplatinum a tetragonal species near PtFe. Minor Ir, Rh, Os and Pd count as Pt; minor Cu and Ni count as Fe. If only compositional data are known, the general name is platinum-iron alloy or Pt–Fe alloy.
Worked on the sheet’s three analyses. The sheet prints each as atomic proportions. Nizhni Tagil, Russia: Pt0.79Fe0.16Rh0.02Pd0.02Cu0.01, so 83.0% platinum-group atoms, above the line, though Pt alone is 79.0%; native platinum. Chocó, Colombia: Pt0.71Fe0.22Rh0.02Cu0.02Ir0.01Os0.01Pd0.01, 76.0% and 24.0% Fe plus Cu: ferroan platinum. Birbir River, Ethiopia: Pt0.56Fe0.40 with 0.04 of Rh, Ir, Os and Pd, 60.0% and 40.0% Fe: ferroan platinum. Recomputed from the weight percentages the figures are 82.9%, 75.3% and 59.1%, the same verdicts. Substitute any analysis in the same sum.
Documented limit: the X-ray clause. The same paper defines isoferroplatinum with no definite compositional limits, and gives a grain with 82.1 atomic % platinum-group elements that a primitive cubic X-ray pattern identified as isoferroplatinum, not native platinum. An analysis alone therefore cannot settle the name; the 1975 paper asks for Pt–Fe alloy until the structure is known. It also says the names polyxene and ferroplatinum should no longer be used; what such old labels mean now is on is platinum a mineral.
Platinum, isoferroplatinum and the Pt–Fe ladder
Three IMA rows are written in platinum and iron alone, and platinum by mass falls from 91.29% to 53.80% down them. The September 2026 list, scanned by script, gives isoferroplatinum, Pt3Fe (A, 1974-012a, Canada), tetraferroplatinum, PtFe (A, 1974-012b, South Africa) and sidorovite, PtFe3 (A, 2022-056, Russia). Worked on standard atomic weights they are 91.29%, 77.74% and 53.80% platinum; the isoferroplatinum sheet prints 91.29 for its ideal. Tulameenite, Pt2CuFe (A, 1972-016, Canada), is 76.57%. Sidorovite has no Handbook sheet; the fetch returned a 404 page and none of its properties are used.
The magnet ledger, as printed. Platinum: nonmagnetic to distinctly magnetic when rich in iron. Tetraferroplatinum: ferromagnetic. Tulameenite: distinctly ferromagnetic. Isoferroplatinum and sperrylite print nothing on magnetism. Cabri and Feather add that the high-iron varieties will have increasing magnetic susceptibility. Neither source tests a hand magnet; the site-wide magnet question is on which minerals are magnetic.
What grows with it. The platinum sheet’s associates are Pt–Fe alloys, chalcopyrite, chromite and magnetite. The isoferroplatinum sheet adds iridium, osmium, braggite, sperrylite and gold, and records it in Pt–Fe and Cu–Ni sulfide deposits in ultramafic rocks and in placers derived from them. Sperrylite, PtAs2, is the one its own sheet calls the most widespread platinum mineral, occurring in every type of deposit: cubic, brittle, hardness 6 to 7, tin-white with a black streak, density 10.58.
Where platinum is found, and why a balance cannot tell it from gold
The Distribution field says platinum comes from many deposits world-wide: the Pinto River, near Papayan, Chocó, Colombia [TL]; in the USA, Platinum Creek, Goodnews Bay, Alaska, a number of California placers such as Trinity County and Oroville, and Cape Blanco, Port Orford, Oregon; in Canada, Rivière-du-Loup and Rivière des Plantes, Quebec, the Fraser and Tranquille Rivers in the Kamloops district, and Granite, Cedar and Olivine Creeks on the Tulameen River, British Columbia, and near Edmonton, Alberta; a large district surrounding Nizhni Tagil in the Urals and good crystals from the Konder massif, Aldan Shield, Sakha; and deposits along the Merensky Reef of the Bushveld complex, South Africa. Its occurrence line: chiefly in placers, or in mafic and ultramafic igneous rocks, rarely in hydrothermal quartz veins or contact metamorphic deposits.
Documented failure: platinum against gold in water. Worked as 20 − 20/D, a 20.00 g piece reads 18.57 to 18.95 g in water as platinum and 18.96 g as gold, the figure on is gold a mineral: 0.01 g apart at the top of platinum’s range. Native silver, 18.02 to 18.20 g, is at least 0.37 g lighter, and native copper 17.77 g. Sperrylite reads 18.11 g, inside silver’s window. The method is on how to measure specific gravity at home; colour and streak do the separating that weight cannot.
Hardness and tenacity agree. Platinum at 4 to 4.5 is harder than gold and silver, both 2.5 to 3 on their sheets, and it is malleable and ductile where sperrylite is brittle. The scratch method is on how to test mineral hardness properly. 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.