Cualstibite is a rare secondary copper mineral that typically forms as delicate blue platy or tabular crystals. It is most commonly found in the oxidized zones of copper-antimony ore deposits where it is often associated with other rare copper minerals.

Hardness

Mohs

Luster

Vitreous

Streak

Pale blue

Transparency

Transparent to translucent

mineralrare

Cualstibite

Hardness: ~2
Luster: Vitreous
Streak: Pale blue
Transparency: Transparent to translucent

Is this cualstibite?

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 cualstibite with a known reference. Cualstibite sits at Mohs ~2, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: pale blue.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: blue green.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: massive, microscopic crystals.

Often confused with

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

mineral

Connellite

Mohs 3

How to tell apart: Connellite is the harder of the two (Mohs 3 vs. ~2).

Often found alongside cualstibite

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

All properties

Chemical formula: Cu₂AlSb(OH)₁₂
Mohs hardness: ~2
Density: 3.18 g/cm³
Colors: Blue green
Streak: Pale blue
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Hexagonal
Crystal habit: Massive, microscopic crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A secondary mineral from oxidation of a hydrothermal polymetallic barite–fluorite deposit

Where rockhounds find cualstibite

Classic worldwide localities

Clara mine, near Oberwolfach, Black Forest, Germany

Field-hunting tip

Where it forms: A secondary mineral from oxidation of a hydrothermal polymetallic barite–fluorite deposit. If you start seeing cornwallite, arsenogoyazite, goethite in float, you are in the right ground. Typical habit: massive, microscopic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cualstibite?+

Mohs hardness is ~2. Luster: vitreous. The streak is pale blue. Common colors include blue green.

Where is cualstibite found?+

Notable localities include Clara mine, near Oberwolfach, Black Forest, Germany.

Is cualstibite safe to handle?+

Cualstibite contains antimony and copper. Contains copper and antimony; wash hands thoroughly after handling and avoid inhaling dust or ingestion.

What rocks look like cualstibite?+

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

What minerals are found with cualstibite?+

Cualstibite commonly co-occurs with Cornwallite, Arsenogoyazite, Goethite, Barite, Fluorite, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cualstibite form in?+

Where it forms: A secondary mineral from oxidation of a hydrothermal polymetallic barite–fluorite deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is cualstibite used for?+

Cualstibite is used in collector.

Find cualstibite on the map

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