Willyamite is a very rare member of the cobaltite group, found primarily in hydrothermal ore deposits. It typically appears as massive or granular metallic aggregates that are difficult to distinguish from other sulfosalt minerals without chemical analysis.

Hardness

5-5.5

Mohs

Luster

Metallic

Streak

Grayish black

Transparency

Opaque

mineralrareCobaltite Group family

Willyamite

Hardness: 5-5.5
Luster: Metallic
Streak: Grayish black
Transparency: Opaque

Is this willyamite?

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 willyamite with a known reference. Willyamite 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: grayish 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: steel gray, silver white.
5
Look at form & habit
Crystal system: cubic. Typical habit: pseudo cubic.

Often confused with

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

Often found alongside willyamite

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

All properties

Chemical formula: Co(SbS)
Mohs hardness: 5-5.5
Density: 6.76 g/cm³
Colors: Steel gray Silver white
Streak: Grayish black
Luster: Metallic
Transparency: Opaque
Crystal system: Cubic
Crystal habit: Pseudo cubic
Cleavage: Perfect on {001}
Rarity: Rare
Uses: Collector, Scientific research
Host rock: In calcite–siderite veins

Where rockhounds find willyamite

Classic worldwide localities

Consols lode, Broken Hill, Willyama Township, New South Wales, Australia

Field-hunting tip

Where it forms: In calcite–siderite veins. If you start seeing dyscrasite, costibite, calcite in float, you are in the right ground. Typical habit: pseudo cubic. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify willyamite?+

Mohs hardness is 5-5.5. Luster: metallic. The streak is grayish black. Common colors include steel gray, silver white.

Where is willyamite found?+

Notable localities include Consols lode, Broken Hill, Willyama Township, New South Wales, Australia.

Is willyamite safe to handle?+

Willyamite contains antimony and cobalt. Contains cobalt, nickel, antimony, and sulfur; handle with care to avoid inhalation of dust or ingestion. Wash hands thoroughly after handling.

What rocks look like willyamite?+

Willyamite is most often confused with Cobaltite, Gersdorffite, Ullmannite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with willyamite?+

Willyamite commonly co-occurs with Dyscrasite, Costibite, Calcite, Siderite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does willyamite form in?+

Where it forms: In calcite–siderite veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is willyamite used for?+

Willyamite is used in collector, scientific research.

Find willyamite on the map

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