Irarsite is a very rare platinum-group mineral typically found in heavy mineral concentrates of alluvial deposits or ultramafic complexes. It is a metallic mineral identified by its distinct silver-white color and high density, often requiring X-ray diffraction or microprobe analysis to distinguish it from other rare platinum-group species.
Is this irarsite?
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 irarsite with a known reference. Irarsite sits at Mohs 6.5, 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: iron black.
- 5Look at form & habitCrystal system: cubic. Typical habit: small euhedral crystals, granular, massive.
Often confused with
Irarsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Irarsite is noticeably harder (Mohs 6.5 vs. 5.5); streak differs, so Irarsite leaves black, Cobaltite leaves grayish black.
How to tell apart: Irarsite is noticeably harder (Mohs 6.5 vs. 5.5); streak differs, so Irarsite leaves black, Gersdorffite leaves grayish black.
How to tell apart: Streak differs, so Irarsite leaves black, Hollingworthite leaves grayish-black.
Often found alongside irarsite
Minerals reported to co-occur with irarsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- IrAsS
- Mohs hardness
- 6.5
- Density
- 11.92 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Small euhedral crystals, granular, massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In chromite in hortonolite dunite (South Africa); as inclusions in chrompicotites (Bulgaria); and as rims around Pt-group alloys
Where rockhounds find irarsite
Classic worldwide localities
- American River, Sacramento Co., and in the Stanislaus River near Knight’s Ferry, Stanislaus Co., California, USA
- Fox Gulch, Goodnews Bay, Alaska, USA
- Merensky Reef, Bushveld complex, Transvaal, from the Onverwacht (type locality) and Driekop mines, South Africa
- Hitura Ni–Cu deposit, western Finland
- Vourinos, Greece
- Pletene chromite deposit, Bulgaria
Field-hunting tip
Where it forms: In chromite in hortonolite dunite (South Africa); as inclusions in chrompicotites (Bulgaria); and as rims around Pt-group alloys. If you start seeing platinum, ruthenian hollingworthite, sperrylite in float, you are in the right ground. Typical habit: small euhedral crystals, granular, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify irarsite?+
Where is irarsite found?+
Is irarsite safe to handle?+
What rocks look like irarsite?+
What minerals are found with irarsite?+
What kind of rock does irarsite form in?+
What is irarsite used for?+
Find irarsite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
