Cupropolybasite is a rare silver-copper sulfosalt member of the polybasite group that occurs in low-temperature hydrothermal veins. It is typically identified by its dark, metallic luster and its association with other silver-bearing minerals, often requiring X-ray diffraction or chemical analysis to distinguish definitively from other polybasite-group minerals.

Hardness

3-3.5

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrarePolybasite Group family

Cupropolybasite

Hardness: 3-3.5
Luster: Metallic
Streak: Black
Transparency: Opaque

Is this cupropolybasite?

4-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 cupropolybasite with a known reference. Cupropolybasite sits at Mohs 3-3.5, 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
Look at form & habit
Crystal system: trigonal. Typical habit: tabular crystals, massive, granular.

Often confused with

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

How to tell apart: Streak differs, so Cupropolybasite leaves black, Stephanite leaves iron-black.

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Often found alongside cupropolybasite

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

All properties

Chemical formula: [Cu₆Sb₂S₇][Ag₉CuS₄]
Mohs hardness: 3-3.5
Density: 6.310 g/cm³
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Trigonal
Crystal habit: Tabular crystals, massive, granular
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Supergene, in a hydrothermal epithermal silver-gold deposit

Where rockhounds find cupropolybasite

Classic worldwide localities

Premier mine, British Columbia, Canada

Field-hunting tip

Where it forms: Supergene, in a hydrothermal epithermal silver-gold deposit. If you start seeing silver, quartz in float, you are in the right ground. Typical habit: tabular crystals, massive, granular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cupropolybasite?+

Mohs hardness is 3-3.5. Luster: metallic. The streak is black.

Where is cupropolybasite found?+

Notable localities include Premier mine, British Columbia, Canada.

Is cupropolybasite safe to handle?+

Cupropolybasite contains antimony and copper. Contains arsenic and copper; wash hands thoroughly after handling and avoid inhaling dust when cleaning or prepping specimens.

What rocks look like cupropolybasite?+

Cupropolybasite is most often confused with Polybasite, Pearceite, Stephanite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with cupropolybasite?+

Cupropolybasite commonly co-occurs with Silver, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cupropolybasite form in?+

Where it forms: Supergene, in a hydrothermal epithermal silver-gold deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is cupropolybasite used for?+

Cupropolybasite is used in collector.

Find cupropolybasite on the map

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