Cornubite is a rare copper arsenate mineral often found as small, crusty, or botryoidal growths in the oxidized zones of ore deposits. It is visually similar to its dimorph, cornwallite, and collectors should look for its distinctive green, fibrous, or radial habits typically found alongside other secondary copper minerals.
Is this cornubite?
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 cornubite with a known reference. Cornubite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Cornubite leaves a pale green streak.
- 3Read the lusterHold the specimen under a strong light. Cornubite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: green, dark green, yellow-green.
- 5Look at form & habitCrystal system: triclinic. Typical habit: botryoidal, crusts, radial aggregates, fibrous.
Often confused with
Cornubite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Cornubite leaves pale green, Olivenite leaves olive-green; luster reads vitreous on Cornubite and adamantine on Olivenite.
How to tell apart: Streak differs — Cornubite leaves pale green, Malachite leaves light green.
Often found alongside cornubite
Minerals reported to co-occur with cornubite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₅(AsO₄)₂(OH)₄
- Mohs hardness
- 3-4
- Density
- 4.2 g/cm³
- Streak
- Pale Green
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Botryoidal, Crusts, Radial Aggregates, Fibrous
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Copper-arsenic Mineral Deposits
- Typical price
- $20-200 depending on specimen size and quality
Where rockhounds find cornubite
Classic worldwide localities
- Cornwall, England
- Lavrion District, Greece
- Black Forest, Germany
- Copiapó, Chile
Field-hunting tip
Look in oxidized zones of copper-arsenic mineral deposits country — that is the host setting where cornubite typically forms. If you start seeing olivenite, cornwallite, conichalcite in float, you are in the right ground. Field specimens usually show a botryoidal, crusts, radial aggregates, fibrous habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cornubite?+
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Find cornubite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
