Cooperite is a rare platinum sulfide mineral typically occurring as microscopic inclusions within magmatic sulfide deposits. Collectors prize it as one of the primary ore minerals for platinum, usually appearing as dull metallic grains in matrix rock.
Is this cooperite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch cooperite with a known reference. Cooperite sits at Mohs 4-5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: steel gray.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: irregular grains, small prismatic crystals.
Often confused with
Cooperite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Sperrylite is the harder of the two (Mohs 6-7 vs. 4-5).
How to tell apart: Laurite is the harder of the two (Mohs 7.5 vs. 4-5); streak differs, so Cooperite leaves black, Laurite leaves dark gray.
How to tell apart: Pyrite is the harder of the two (Mohs 6-6.5 vs. 4-5); streak differs, so Cooperite leaves black, Pyrite leaves greenish black to brownish black.
Often found alongside cooperite
Minerals reported to co-occur with cooperite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- PtS
- Mohs hardness
- 4-5
- Density
- 9.5 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Irregular grains, small prismatic crystals
- Cleavage
- {011}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A significant platinum ore mineral, found in ultramafics, gabbros, dunites, chromitites, typically layered; in massive chalcopyrite–pyrrhotite orebodies; in alluvial placers
Where rockhounds find cooperite
Classic worldwide localities
- Stillwater complex, Montana, USA
- Junction of the Trinity and Klamath Rivers, Humboldt Co., and from the Merced River at Snelling and Cressy, Merced Co., California, USA
- Rustenburg (type locality) and Potgietersrus districts, and various other localities along the Merensky Reef of the Bushveld complex, Transvaal, South Africa
- Freetown complex, Sierra Leone
- Lac des Iles complex, Ontario, and the Tulameen district, British Columbia, Canada
- Severnyi mine, Noril’sk region, western Siberia, Russia
Field-hunting tip
Where it forms: A significant platinum ore mineral, found in ultramafics, gabbros, dunites, chromitites, typically layered; in massive chalcopyrite–pyrrhotite orebodies; in alluvial placers. If you start seeing braggite, vysotskite, sperrylite in float, you are in the right ground. Typical habit: irregular grains, small prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find cooperite on the map
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