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, 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.