Stillwaterite is a very rare palladium arsenide typically found as microscopic grains within platinum-group element deposits. Collectors prize it primarily as a rare ore mineral associated with ultramafic layered intrusions like the Stillwater Complex.

Hardness

4-4.5

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrare

Stillwaterite

Hardness: 4-4.5
Luster: Metallic
Streak: Black
Transparency: Opaque

No image

Is this stillwaterite?

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 stillwaterite with a known reference. Stillwaterite sits at Mohs 4-4.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Stillwaterite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Stillwaterite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: white, pale yellow.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: anhedral grains.

Often confused with

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

Often found alongside stillwaterite

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

All properties

Chemical formula: Pd₈As₃
Mohs hardness: 4-4.5
Density: 9.43 g/cm³
Colors: White Pale Yellow
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Hexagonal
Crystal habit: Anhedral Grains
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Mafic and Ultramafic Igneous Rocks
Typical price: $50-300 per micro-specimen

Where rockhounds find stillwaterite

Classic worldwide localities

Stillwater Complex, Montana, USA
Norilsk, Russia

Field-hunting tip

Look in mafic and ultramafic igneous rocks country — that is the host setting where stillwaterite typically forms. If you start seeing palladium, platinum, sperrylite in float, you are in the right ground. Field specimens usually show a anhedral grains habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify stillwaterite?+

Mohs hardness is 4-4.5. It typically shows a metallic luster. The streak is black. Common colors include white, pale yellow.

Where is stillwaterite found?+

Notable localities include Stillwater Complex, Montana, USA; Norilsk, Russia.

How much is stillwaterite worth?+

Typical asking prices fall in the range of $50-300 per micro-specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is stillwaterite safe to handle?+

It contains toxic constituents. Contains arsenic, which is toxic if inhaled or ingested. Wash hands thoroughly after handling and avoid creating dust or powder. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like stillwaterite?+

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

What minerals are found with stillwaterite?+

Stillwaterite commonly co-occurs with Palladium, Platinum, Sperrylite, Chalcopyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does stillwaterite form in?+

Stillwaterite typically forms in mafic and ultramafic igneous rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is stillwaterite used for?+

Stillwaterite is used in collector.

Find stillwaterite on the map

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