Iridosmine is a rare natural alloy of osmium and iridium, typically found as small, heavy, metallic flakes in alluvial placer deposits. Due to its extreme hardness and resistance to chemical weathering, it accumulates in river sediments alongside other platinum-group metals.
Is this iridosmine?
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 iridosmine with a known reference. Iridosmine sits at Mohs 6-7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: gray.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: small flattened hexagonal plates, scales, or rounded grains.
Often confused with
Iridosmine vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Iridosmine is noticeably harder (Mohs 6-7 vs. 4-4.5); streak differs, so Iridosmine leaves gray, Platinum leaves grayish white.
How to tell apart: Iridosmine is noticeably harder (Mohs 6-7 vs. 4.5-5); streak differs, so Iridosmine leaves gray, Palladium leaves silver-white.
How to tell apart: Streak differs, so Iridosmine leaves gray, Sperrylite leaves black.
Often found alongside iridosmine
Minerals reported to co-occur with iridosmine. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Os,Ir)
- Mohs hardness
- 6-7
- Density
- 22.15 g/cm³
- Colors
- Streak
- Gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Hexagonal
- Crystal habit
- Small flattened hexagonal plates, scales, or rounded grains
- Cleavage
- Perfect but difficult on {0001}
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- In magmatic segregation deposits, and concentrated into placers on their reduction by weathering
Where rockhounds find iridosmine
1 mapped spotsClassic worldwide localities
- Ruby Creek, British Columbia, Canada
- Atlin district, British Columbia, Canada
- Spruce Creek, British Columbia, Canada
- Granite Creek, in the Thlameen River area, British Columbia, Canada
- Heazlewood Complex and the Adamsfield district, Tasmania, Australia
- Guma Water placers, Sierra Leone
Field-hunting tip
Where it forms: In magmatic segregation deposits, and concentrated into placers on their reduction by weathering. If you start seeing osmiridium, irarsite, laurite in float, you are in the right ground. Typical habit: small flattened hexagonal plates, scales, or rounded grains. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Washington. Start trip planning there.
Common questions
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Find iridosmine on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
