Iridarsenite is a very rare platinum-group mineral typically occurring as microscopic anhedral grains in platinum-group element deposits. It is most frequently identified in polished sections during ore microscopy due to its extremely small grain size and association with other platinum-group minerals.

Hardness

5-5.5

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrare

Iridarsenite

Hardness: 5-5.5
Luster: Metallic
Streak: Black
Transparency: Opaque

Is this iridarsenite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch iridarsenite with a known reference. Iridarsenite sits at Mohs 5-5.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: black.
3
Read the luster
Hold the specimen under a strong light. Luster: metallic.
4
Match the color range
Compare against the expected color range: gray.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: anhedral grains.

Often confused with

Iridarsenite vs. its common look-alikes, and how to tell them apart in the field.

How to tell apart: Streak differs, so Iridarsenite leaves black, Hollingworthite leaves grayish-black.

Compare →

Often found alongside iridarsenite

Minerals reported to co-occur with iridarsenite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: IrAs₂
Mohs hardness: 5-5.5
Density: 10.9 g/cm³
Colors: Gray
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Anhedral grains
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In nuggets or fragments of natural Os–Ir–Ru alloys

Where rockhounds find iridarsenite

Classic worldwide localities

Fox Gulch, Goodnews Bay, Alaska, USA
Merensky Reef, Bushveld complex, Witwatersrand, Transvaal, South Africa
Zlatoust, Ural Mountains, Russia
Placers at Anduo, Tibet, China

Field-hunting tip

Where it forms: In nuggets or fragments of natural Os–Ir–Ru alloys. If you start seeing irarsite, ruthenarsenite, rutheniridosmine in float, you are in the right ground. Typical habit: anhedral grains. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify iridarsenite?+

Mohs hardness is 5-5.5. Luster: metallic. The streak is black. Common colors include gray.

Where is iridarsenite found?+

Notable localities include Fox Gulch, Goodnews Bay, Alaska, USA; Merensky Reef, Bushveld complex, Witwatersrand, Transvaal, South Africa; Zlatoust, Ural Mountains, Russia; Placers at Anduo, Tibet, China.

Is iridarsenite safe to handle?+

Iridarsenite contains arsenic and calls for real care. Contains arsenic; handle with care and avoid inhalation of dust during processing or cleaning.

What rocks look like iridarsenite?+

Iridarsenite is most often confused with Sperrylite, Hollingworthite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with iridarsenite?+

Iridarsenite commonly co-occurs with Irarsite, Ruthenarsenite, Rutheniridosmine. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does iridarsenite form in?+

Where it forms: In nuggets or fragments of natural Os–Ir–Ru alloys. Working float back to the host body is the standard way to chase a fresh occurrence.

What is iridarsenite used for?+

Iridarsenite is used in collector.

Find iridarsenite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.