Cornetite is an uncommon copper phosphate mineral typically found as deep blue, radiating sprays or crusts in the oxidized zones of copper ore bodies. Collectors look for its vivid, intense blue color and distinctive acicular crystal sprays, often occurring alongside other secondary copper minerals like malachite.
Is this cornetite?
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 cornetite with a known reference. Cornetite sits at Mohs ~4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale blue.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark blue, greenish blue.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular crystals, radiating sprays, globular crusts.
Often confused with
Cornetite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside cornetite
Minerals reported to co-occur with cornetite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₃(PO₄)(OH)₃
- Mohs hardness
- ~4.5
- Density
- 4.10 g/cm³
- Colors
- Streak
- Pale blue
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular crystals, radiating sprays, globular crusts
- Cleavage
- Distinct on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in the oxidized zone of some hydrothermal copper deposits
Where rockhounds find cornetite
Classic worldwide localities
- Blue Jay and Empire-Nevada mines, Yerington district, Lyon Co., USA
- Tyrone, Santa Rita, Grant Co., New Mexico, USA
- Saginaw Hill, Pima Co., Arizona, USA
- Star of the Congo mine, near Lubumbashi, and at the Kalabi and Lukini mines, Katanga Province, Congo (Shaba Province, Zaire)
- Bwana Mkubwa mine, Ndola, and Kansanshi, Zambia
- Alaska, Mangula, and Molly mines, Lomagundi district, Zimbabwe
Field-hunting tip
Where it forms: A rare secondary mineral in the oxidized zone of some hydrothermal copper deposits. If you start seeing copper, brochantite, pseudomalachite in float, you are in the right ground. Typical habit: acicular crystals, radiating sprays, globular crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cornetite?+
Where is cornetite found?+
Is cornetite safe to handle?+
What rocks look like cornetite?+
What minerals are found with cornetite?+
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What is cornetite used for?+
Find cornetite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
