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

Translucent

mineralrare

Cualstibite

Hardness: 2
Luster: Vitreous
Streak: Pale Blue
Transparency: 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. Cualstibite leaves a pale blue streak.
3
Read the luster
Hold the specimen under a strong light. Cualstibite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: blue, greenish-blue.
5
Look at form & habit
Crystal system: trigonal. Typical habit: platy crystals, tabular aggregates.

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).

How to tell apart: Streak differs, so Cualstibite leaves pale blue, Spangolite leaves pale green.

Compare →

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: Cu₄Sb(OH)₁₂Cl
Mohs hardness: 2
Density: 3.32 g/cm³
Colors: Blue Greenish-blue
Streak: Pale Blue
Luster: Vitreous
Transparency: Translucent
Crystal system: Trigonal
Crystal habit: Platy Crystals, Tabular Aggregates
Cleavage: Perfect Basal
Rarity: Rare
Uses: Collector
Host rock: Oxidized Copper Deposits

Where rockhounds find cualstibite

Classic worldwide localities

Clara mine, Black Forest, Germany

Field-hunting tip

Look in oxidized copper deposits country, the host setting where cualstibite typically forms. If you start seeing malachite, brochantite, connellite in float, you are in the right ground. Field specimens usually show a platy crystals, tabular aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cualstibite?+

Mohs hardness is 2. It typically shows a vitreous luster. The streak is pale blue. Common colors include blue, greenish-blue.

Where is cualstibite found?+

Notable localities include Clara mine, Black Forest, Germany.

Is cualstibite safe to handle?+

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

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 Malachite, Brochantite, Connellite, Tenorite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cualstibite form in?+

Cualstibite typically forms in oxidized copper deposits. 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.