Chalcoalumite is a rare secondary copper mineral that typically forms as delicate, sky-blue crusts or velvety coatings in oxidized ore deposits. It is most frequently found in the weathered zones of copper mines where it often accompanies other bright blue or green copper carbonates and sulfates.
Is this chalcoalumite?
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 chalcoalumite with a known reference. Chalcoalumite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to dull.
- 4Match the color rangeCompare against the expected color range: blue, blue gray, greenish blue, light blue green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: encrustations, fibrous.
Often confused with
Chalcoalumite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside chalcoalumite
Minerals reported to co-occur with chalcoalumite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuAl₄(SO₄)(OH)₁₂·3H₂O
- Mohs hardness
- 2.5
- Density
- 2.29 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous to dull
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Encrustations, fibrous
- Cleavage
- On {100}, perfect
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- A rare secondary mineral in the oxidized portions of copper deposits
Where rockhounds find chalcoalumite
Classic worldwide localities
- Bisbee, Cochise Co., and in the Grandview mine, Grand Canyon, Coconino Co., Arizona, USA
- Titusville mine, head of Kendall Gulch, San Juan Co., Colorado, USA
- Lovelock mine, Table Mountain district, Churchill Co., Nevada, USA
- Spatsum claim, south of Ashcroft Manor, British Columbia, Canada
- Britannia mine, Snowdonia, Gwynedd, Wales
- South Wheal Crebor, Tavistock, Devon, and in the Penberthy Croft mine, St. Hilary, Cornwall, England
Field-hunting tip
Where it forms: A rare secondary mineral in the oxidized portions of copper deposits. If you start seeing cuprite, malachite, azurite in float, you are in the right ground. Typical habit: encrustations, fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify chalcoalumite?+
Where is chalcoalumite found?+
Is chalcoalumite safe to handle?+
What rocks look like chalcoalumite?+
What minerals are found with chalcoalumite?+
What kind of rock does chalcoalumite form in?+
What is chalcoalumite used for?+
Find chalcoalumite on the map
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