Ceruleite is a rare copper aluminum arsenate mineral typically found as soft, sky-blue massive crusts or botryoidal forms within oxidized copper deposits. Collectors value it for its vibrant color, though it is usually opaque and requires careful handling due to its arsenic content.
Is this ceruleite?
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 ceruleite with a known reference. Ceruleite sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: bluish white.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: blue, deep blue.
- 5Look at form & habitCrystal system: triclinic. Typical habit: massive, crusts, botryoidal.
Often confused with
Ceruleite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ceruleite leaves bluish white, Turquoise leaves white to pale greenish blue; luster reads dull on Ceruleite and vitreous in crystals; dull to waxy if massive on Turquoise.
How to tell apart: Ceruleite is noticeably harder (Mohs 5-6 vs. ~2-4); streak differs, so Ceruleite leaves bluish white, Chrysocolla leaves white when pure; luster reads dull on Ceruleite and vitreous, porcelaneous, earthy on Chrysocolla.
How to tell apart: Streak differs, so Ceruleite leaves bluish white, Variscite leaves white; luster reads dull on Ceruleite and vitreous to waxy on Variscite.
Often found alongside ceruleite
Minerals reported to co-occur with ceruleite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuAl₄(AsO₄)₂(OH)₈(H₂O)₄
- Mohs hardness
- 5-6
- Density
- 2.70-2.80 g/cm³
- Streak
- Bluish white
- Luster
- Dull
- Transparency
- Semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Massive, crusts, botryoidal
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Lapidary
- Host rock
- In the oxidized zone of arsenic-rich polymetallic mineral deposits; a post-mine product
Where rockhounds find ceruleite
Classic worldwide localities
- Emma Louisa gold mine, Guanaco district, about 100 km east-northeast of Taltal, Antofagasta, Chile
- Wheal Gorland and Wheal Maid, Gwennap, and in the Penberthy Croft mine, St. Hilary, Cornwall, England
- Cap Garonne mine, near Le Pradet, Var, France
- Anticline prospect, 11 km west-southwest of Ashburton Downs homestead, Capricorn Range, Western Australia
- Tsumeb, Namibia
Field-hunting tip
Where it forms: In the oxidized zone of arsenic-rich polymetallic mineral deposits; a post-mine product. If you start seeing alumopharmacosiderite, olivenite, schlossmacherite in float, you are in the right ground. Typical habit: massive, crusts, botryoidal. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ceruleite?+
Where is ceruleite found?+
Is ceruleite safe to handle?+
What rocks look like ceruleite?+
What minerals are found with ceruleite?+
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Find ceruleite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
