Sperrylite
Sperrylite, PtAs2: cubic platinum arsenide, hardness 6 to 7, density 10.58, tin-white with a black streak, 56.56% Pt. Type locality the Vermilion mine, Sudbury.
Sperrylite is platinum arsenide, PtAs2, an IMA species (G, 1889, Canada): cubic, in cubes and cubo-octahedrons to 5 cm, hardness 6 to 7, density 10.58, tin-white with a black streak. It is 56.56% platinum by mass. Of the 11 IMA minerals made of one metal and two arsenic atoms, it is the only platinum one and the only pyrite-group one on its sheet.
In short
- The diarsenide ledger. A row parser and an independent field scan of the September 2026 IMA-CNMNC Master List both find 11 rows written as one metal plus As2. Worked on standard atomic weights, sperrylite (PtAs2) is 56.56% metal, ahead of iridarsenite (IrAs2) 56.19%, omeiite (OsAs2) 55.94%, anduoite (RuAs2) 40.28%, and the iron, cobalt, nickel and copper diarsenides at 27.15 to 29.78%.
- Cubic, and pyrite group, on its sheet. Of the 11 Handbook of Mineralogy sheets for those rows, two print cubic, sperrylite and krutovite (NiAs2), and one prints Pyrite group: sperrylite. The others are orthorhombic or monoclinic; the löllingite and rammelsbergite sheets print Löllingite group, clinosafflorite’s Arsenopyrite group.
- The Ni–Cu ore weight check. Worked as 20 − 20/D, a 20.00 g sperrylite crystal reads 18.11 g in water. The base-metal minerals on its sheet’s association line read lower: galena 17.36 g, gersdorffite 16.61 g, pyrite 16.01 g, pentlandite 15.65 to 16.00 g. Documented failure: its platinum-group associates do not: cooperite reads 17.89 g, only 0.22 g under, and omeiite 18.21 g on a calculated density.
- Grains, not crystals, in most ore. The USGS Professional Paper 1802-N says platinum-group minerals in most rocks range from less than a micron to a few hundred microns, and that most geologists can spend a lifetime on PGE-rich rocks and never see one in a hand specimen. The weight check is for crystals only.
- Where. The Distribution field names the Vermilion [TL], Victoria and Frood mines near Sudbury, Ontario; the Merensky reef of the Bushveld complex, with fine crystals from Tweefontein Farm; the Stillwater complex, Montana; Talnakh, Noril’sk, for large crystals; Kambalda, Western Australia; and Danba, Sichuan, among others.
| Name | Formula (IMA) | IMA status | Metal by mass | System (sheet) | Group (sheet) | Hardness (sheet) | Density (sheet) | 20.00 g piece in water |
|---|---|---|---|---|---|---|---|---|
| Sperrylite | PtAs2 | G, 1889, Canada | Pt 56.56% | Cubic | Pyrite group | 6 to 7 | 10.58 | 18.11 g |
| Iridarsenite | IrAs2 | A, 1973-021 | Ir 56.19% | Monoclinic | Not printed | n.d. (VHN 488 and 686) | n.d.; calc. 10.9 | 18.17 g (calc.) |
| Omeiite | OsAs2 | A, 1985 | Os 55.94% | Orthorhombic | Not printed | n.d. | n.d.; calc. 11.20 | 18.21 g (calc.) |
| Anduoite | RuAs2 | A | Ru 40.28% | Orthorhombic | Not printed | n.d. | n.d.; calc. 8.692 | 17.70 g (calc.) |
| Paxite | CuAs2 | A, 1967 s.p., Czech Republic | Cu 29.78% | Monoclinic | Not printed | 3.5 to 4 | 5.4 | 16.30 g |
| Safflorite | CoAs2 | G, 1835, Germany | Co 28.23% | Orthorhombic | Not printed | 4.5 to 5 | 7.2 | 17.22 g |
| Clinosafflorite | CoAs2 | A, 1970-014, Canada | Co 28.23% | Monoclinic | Arsenopyrite group | 4.5 to 5 | n.d.; calc. 7.46 | 17.32 g (calc.) |
| Rammelsbergite | NiAs2 | G, 1845, Germany | Ni 28.15% | Orthorhombic | Löllingite group | 5.5 to 6 | 7.1 | 17.18 g |
| Pararammelsbergite | NiAs2 | G, 1940, Canada | Ni 28.15% | Orthorhombic | Not printed | About 5 | 7.12 | 17.19 g |
| Krutovite | NiAs2 | A, 1975-009, Czech Republic | Ni 28.15% | Cubic | Not printed | 5.5 | n.d.; calc. 7.08 to 7.12 | 17.18 to 17.19 g (calc.) |
| Löllingite | FeAs2 | G, 1845, Austria | Fe 27.15% | Orthorhombic | Löllingite group | 5 to 5.5 | 7.40 | 17.30 g |
What is sperrylite? Platinum arsenide, PtAs2
Sperrylite is platinum arsenide with one platinum atom to two of arsenic, PtAs2. The Handbook of Mineralogy sperrylite sheet gives it cubic, point group 2/m −3 (read from the rendered sheet), commonly well crystallised as cubes and cubo-octahedrons to 5 cm, which may be highly modified with rounded edges and corners, and as intergrowths with Pt–Fe alloys. Cleavage is indistinct on {001}, the fracture conchoidal, and it is brittle, with hardness 6 to 7 and Vickers 960 to 1277 at a 100 g load. It is opaque, tin-white, with a black streak and a metallic lustre. Measured density is 10.58 and calculated 10.78.
What the IMA list records. The September 2026 list gives sperrylite, PtAs2, status G (grandfathered, described before the IMA existed), 1889, with Canada as the country of first description and a second reference of Canadian Mineralogist 17 (1979), 117. The sheet marks the Vermilion mine near Sudbury, Ontario, as the type locality and names the mineral for Francis Lewis Sperry (1861–1906), chemist of Sudbury, who first found it.
Its chemistry, worked. On standard atomic weights PtAs2 has a formula mass of 344.93: 56.56% platinum and 43.44% arsenic, the ideal figures the sheet prints. The sheet’s microprobe analysis from the Vermilion mine reads Pt 56.8, As 42.8, Sb 0.08, which works out at 1.96 arsenic atoms to each platinum against the ideal 2; the sheet writes it as Pt1.01As1.96. Sperrylite contains arsenic; any question about handling arsenic minerals belongs on toxic minerals in a collection, and nothing on this page is health or safety advice.
Is sperrylite in the pyrite group? The diarsenide ledger
On its sheet, yes: sperrylite is the one platinum mineral of the 11 IMA diarsenides, and the only one of the 11 whose Handbook sheet prints Pyrite group. The IMA list has no group column, so the group comes from the sheet; the pyrite sheet prints Pyrite group as well, for FeS2.
Method. The September 2026 list was converted with pdftotext -layout. A row parser read name, formula and status from each line; an independent scan split every line on runs of two or more spaces and took the second field as the formula. Both kept formulas of exactly one metal symbol followed by As2, and both found the same 11 rows: sperrylite, iridarsenite, omeiite, anduoite, paxite, safflorite, clinosafflorite, rammelsbergite, pararammelsbergite, krutovite and löllingite. The Handbook sheet for each of the 11 was then read for crystal system, group, hardness and density.
What the ledger shows. Sperrylite carries the most metal of the 11, 56.56%, just ahead of iridarsenite at 56.19% and omeiite at 55.94%. Its hardness, 6 to 7, is the highest printed on the 11 sheets; three print none. Of the six sheets with a measured density, sperrylite’s 10.58 is the highest; omeiite’s and iridarsenite’s calculated figures, 11.20 and 10.9, are higher, but no measurement is printed for either. Two sheets print cubic, sperrylite and krutovite, and of those only sperrylite’s prints a group. The ledger stands beside the wider list of platinum minerals on is platinum a mineral, which is not repeated here.
How do you tell sperrylite from pyrite, gersdorffite and galena? The Ni–Cu ore weight check
A tin-white, brittle cube that reads 18.11 g in water for every 20.00 g is sperrylite’s figure; of the base-metal minerals on its association line with a sheet read here, none comes within 0.75 g of it. Worked as 20 − 20/D on the sheets’ measured densities: sperrylite 10.58, 18.11 g; galena 7.58, 17.36 g; gersdorffite 5.9, 16.61 g; pyrite 5.018, 16.01 g; pentlandite 4.6 to 5.0, 15.65 to 16.00 g. Two tin-white minerals that are not on its association line read lower too: cobaltite 16.84 g and skutterudite 16.92 g. The method is on how to measure specific gravity at home.
Colour and streak before the balance. The sheets give sperrylite tin-white with a black streak; pyrite pale brass-yellow, pentlandite pale bronze-yellow, galena lead-gray with a lead-gray streak, gersdorffite silver-white to steel-gray with a grayish-black streak. Hardness also helps: sperrylite 6 to 7 against galena 2.5 to 2.75 and pentlandite 3.5 to 4; pyrite, at 6 to 6.5, does not separate by hardness. Streak technique is on how to use a streak plate.
Where the check fails, documented. The platinum-group minerals on the same association line are as heavy as sperrylite. Cooperite, PtS, density 9.5 on its sheet, reads 17.89 g, 0.22 g under. Omeiite and iridarsenite, the osmium and iridium diarsenides, read 18.21 and 18.17 g on their calculated densities and bracket sperrylite’s 18.11 g; their sheets describe crystals to 20 µm and inclusions to 60 µm, so only an analysis separates them. And native platinum itself reads 18.57 to 18.95 g; the comparison between the two is on the platinum page and is not repeated here.
Is sperrylite a platinum ore? What the sources say
No source fetched for this page names sperrylite as an ore of platinum, so this page does not either. The sheet’s Occurrence line calls it the most widespread platinum mineral, occurring in every type of deposit. The USGS Professional Paper 1802-N on the platinum-group elements (Zientek and co-authors, 2017) lists sperrylite, PtAs2, in its Table N1 of platinum-group minerals, under compounds with metalloids; a text search of the chapter finds the word once, in that table.
What the USGS chapter does say. Platinum-group minerals in most rocks are fine-grained, from less than a micron to a few hundred microns across; information about their mineralogy is needed to extract metals from their ore minerals effectively; and platinum-group elements were recovered as a byproduct of nickel mining at Sudbury, where by 1934 Canada had become the leading producer. Sudbury is sperrylite’s type district on the sheet, but the chapter does not tie the two together and nor does this page.
What it grows with. The association line is given by locality. At Danba, China: pyrrhotite, pentlandite, chalcopyrite, violarite, cubanite, bornite, sphalerite, galena, linnaeite, magnetite, testibiopalladite, sudburyite, omeiite, gold and argentian gold. At Shiaonanshan, China: leadamalgam, chromite, ilmenite, magnetite, gersdorffite, pyrite, chalcopyrite, violarite, millerite, galena, stibnite, argentian gold, niggliite, iridosmine, platinum, merenskyite and kotulskite. Also cooperite and laurite.
Where sperrylite is found
The Distribution field names, in Canada, the Vermilion [TL], Victoria and Frood mines, Algoma district, near Sudbury, Ontario. In the USA, the New Rambler Cu–Ni mine, Medicine Bow Mountains, Albany Co., Wyoming; the Key West mine, Clark Co., Nevada; and the Stillwater complex, Montana. In South Africa, the Merensky reef of the Bushveld complex, with fine crystals from the Tweefontein Farm near Potgietersrus, and the Atok, Onverwacht and Rustenburg mines. Also Antamponbato, Madagascar; Danba, Sichuan, and Shiaonanshan, Inner Mongolia, China; several deposits east of Broken Hill, New South Wales, and Kambalda, Western Australia; large crystals from the Talnakh area, Noril’sk, with Nikolaevsky, Amur, and the Konder massif, Sakha, Russia; and Rometölväs Hill, the Hitura Cu–Ni deposit and the Siikakama intrusion, Finland.
Type material is held at the Royal Ontario Museum, Toronto, and at Yale University, New Haven, numbers 1.2950 and 1.5895, per the sheet.
Weighing it. A 20.00 g sperrylite crystal reads 18.11 g in water; sulphide or silicate matrix pulls the reading down. 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.