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, so 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, 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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