Aluminocopiapite is a rare hydrated sulfate mineral that typically forms as yellow efflorescent crusts or powdery aggregates in the oxidation zones of sulfide-rich ore bodies. It is best identified through its association with other secondary sulfate minerals and its distinct, often bright yellow, coloration. Due to its solubility in water, specimens should be stored in a dry, humidity-controlled environment to prevent degradation.
Is this aluminocopiapite?
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 aluminocopiapite with a known reference. Aluminocopiapite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: earthy.
- 4Match the color rangeCompare against the expected color range: yellow.
- 5Look at form & habitCrystal system: triclinic. Typical habit: massive, crusts, tabular crystals.
Often confused with
Aluminocopiapite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Aluminocopiapite leaves light yellow, Copiapite leaves pale yellow; luster reads earthy on Aluminocopiapite and pearly on {010} on Copiapite.
How to tell apart: Streak differs, so Aluminocopiapite leaves light yellow, Fibroferrite leaves white; luster reads earthy on Aluminocopiapite and pearly, silky in aggregates on Fibroferrite.
How to tell apart: Aluminocopiapite is noticeably harder (Mohs 2.5-3 vs. 1.5); streak differs, so Aluminocopiapite leaves light yellow, Halotrichite leaves white; luster reads earthy on Aluminocopiapite and vitreous on Halotrichite.
Often found alongside aluminocopiapite
Minerals reported to co-occur with aluminocopiapite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- AlFe₄(SO₄)₆O(OH)(H₂O)₁₄·6H₂O
- Mohs hardness
- 2.5-3
- Density
- 2.163 g/cm³
- Colors
- Streak
- Light yellow
- Luster
- Earthy
- Transparency
- Semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Massive, crusts, tabular crystals
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral typically formed by the oxidation of pyrite in shales and coal; may be a fumarolic reaction product
Where rockhounds find aluminocopiapite
Classic worldwide localities
- Island Mountain, Trinity Co., and the Champion mine, White Mountains, Mono Co., California, USA
- Coeur d’Alene mine, Central City district, Gilpin Co., Colorado, USA
- Mosquito Fork of the Forty Mile River, Eagle A-3 quadrangle, Alaska, USA
- Cerritos Bayos, southwest of Calama, Antofagasta, Chile
- Cetine mine, 20 km southwest of Siena, Tuscany, and at the Grotto de Faraglione, Port de Levante, Vulcano, Lipari Islands, Italy
- Dolcoath mine, Camborne, Cornwall, England
Field-hunting tip
Where it forms: A secondary mineral typically formed by the oxidation of pyrite in shales and coal; may be a fumarolic reaction product. If you start seeing pyrite in float, you are in the right ground. Typical habit: massive, crusts, tabular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify aluminocopiapite?+
Where is aluminocopiapite found?+
What rocks look like aluminocopiapite?+
What minerals are found with aluminocopiapite?+
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Find aluminocopiapite on the map
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