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.
Is this cualstibite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch cualstibite with a known reference. Cualstibite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Cualstibite leaves a pale blue streak.
- 3Read the lusterHold the specimen under a strong light. Cualstibite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: blue, greenish-blue.
- 5Look at form & habitCrystal 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.
How to tell apart: Connellite is the harder of the two (Mohs 3 vs. 2); luster reads pearly on Cualstibite and vitreous on Connellite.
How to tell apart: Spangolite is the harder of the two (Mohs 3 vs. 2); streak differs — Cualstibite leaves pale blue, Spangolite leaves pale green; luster reads pearly on Cualstibite and vitreous on Spangolite.
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
- Streak
- Pale Blue
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Platy Crystals, Tabular Aggregates
- Cleavage
- Perfect Basal
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Copper Deposits
- Typical price
- $50-300 per specimen depending on size and quality
Where rockhounds find cualstibite
Classic worldwide localities
- Cap Garonne Mine (France)
- Pampa Larga Mine (Chile)
- Broken Hill (Australia)
Field-hunting tip
Look in oxidized copper deposits country — that is 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
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Find cualstibite on the map
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