Cuprostibite is an extremely rare copper antimony mineral typically found as small, non-descript grains within alkaline igneous rocks. It is primarily identified in lab settings due to its subtle metallic appearance and association with exotic minerals in the Ilimaussaq complex.

Hardness

3.5

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrare

Cuprostibite

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

Is this cuprostibite?

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 cuprostibite with a known reference. Cuprostibite sits at Mohs 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. Cuprostibite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Cuprostibite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: dark gray, bronze-like, light red.
5
Look at form & habit
Crystal system: trigonal. Typical habit: massive, anhedral grains, interstitial.

Often confused with

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

mineral

Domeykite

Mohs 3-3.5

How to tell apart: Streak differs — Cuprostibite leaves black, Domeykite leaves metallic white.

Often found alongside cuprostibite

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

All properties

Chemical formula: Cu₂Sb
Mohs hardness: 3.5
Density: 8.84 g/cm³
Colors: Dark Gray Bronze-like Light Red
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Trigonal
Crystal habit: Massive, Anhedral Grains, Interstitial
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Agpaitic Nepheline Syenite Pegmatites
Typical price: $50-300 per micro-mount or small specimen

Where rockhounds find cuprostibite

Classic worldwide localities

Ilimaussaq complex, Greenland
Yukon, Canada

Field-hunting tip

Look in agpaitic nepheline syenite pegmatites country — that is the host setting where cuprostibite typically forms. If you start seeing djerfisherite, villiaumite, sodalite in float, you are in the right ground. Field specimens usually show a massive, anhedral grains, interstitial habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cuprostibite?+

Mohs hardness is 3.5. It typically shows a metallic luster. The streak is black. Common colors include dark gray, bronze-like, light red.

Where is cuprostibite found?+

Notable localities include Ilimaussaq complex, Greenland; Yukon, Canada.

How much is cuprostibite worth?+

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

Is cuprostibite safe to handle?+

It contains toxic constituents. Contains antimony and copper; handle with care and wash hands after handling to avoid ingestion or skin irritation. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like cuprostibite?+

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

What minerals are found with cuprostibite?+

Cuprostibite commonly co-occurs with Djerfisherite, Villiaumite, Sodalite, Galena. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cuprostibite form in?+

Cuprostibite typically forms in agpaitic nepheline syenite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is cuprostibite used for?+

Cuprostibite is used in collector.

Find cuprostibite on the map

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