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

2.5-3

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrarePolybasite Group family

Cupropolybasite

Hardness: 2.5-3
Luster: Metallic
Streak: Black
Transparency: Opaque

Is this cupropolybasite?

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 cupropolybasite with a known reference. Cupropolybasite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Cupropolybasite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Cupropolybasite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: black, iron-black.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals, massive, granular.

Often confused with

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

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: Cu₁₆As₂Sb₂S₁₁
Mohs hardness: 2.5-3
Density: 6.39 g/cm³
Colors: Black Iron-black
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Tabular Crystals, Massive, Granular
Cleavage: Imperfect On {001}
Rarity: Rare
Uses: Collector
Host rock: Epithermal Hydrothermal Veins
Typical price: $20-150 thumbnail to cabinet

Where rockhounds find cupropolybasite

Classic worldwide localities

Veta Rica mine, Mexico
Guanajuato, Mexico
Kongsberg, Norway
Freiberg, Germany

Field-hunting tip

Look in epithermal hydrothermal veins country — that is the host setting where cupropolybasite typically forms. If you start seeing silver, acanthite, galena in float, you are in the right ground. Field specimens usually show a tabular crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cupropolybasite?+

Mohs hardness is 2.5-3. It typically shows a metallic luster. The streak is black. Common colors include black, iron-black.

Where is cupropolybasite found?+

Notable localities include Veta Rica mine, Mexico; Guanajuato, Mexico; Kongsberg, Norway; Freiberg, Germany.

How much is cupropolybasite worth?+

Typical asking prices fall in the range of $20-150 thumbnail to cabinet. Quality, size, and provenance can move individual specimens well outside that range.

Is cupropolybasite safe to handle?+

It contains toxic constituents. Contains arsenic and copper; wash hands thoroughly after handling and avoid inhaling dust when cleaning or prepping specimens. Handle with care, avoid grinding or breathing dust, and store separately.

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, Acanthite, Galena, Sphalerite, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cupropolybasite form in?+

Cupropolybasite typically forms in epithermal hydrothermal veins. 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.