Sieleckiite is a rare copper-aluminum phosphate mineral typically found as small, bright blue botryoidal crusts or spherical aggregates. It is primarily known from the oxidation zones of specific copper mines in Argentina. Collectors prize it for its vibrant color and unique micro-crystalline habit.
Is this sieleckiite?
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 sieleckiite with a known reference. Sieleckiite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Sieleckiite leaves a light blue streak.
- 3Read the lusterHold the specimen under a strong light. Sieleckiite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: blue, azure-blue.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fibrous, spherical, botryoidal crusts.
Often confused with
Sieleckiite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Turquoise is the harder of the two (Mohs 5-6 vs. 3); streak differs — Sieleckiite leaves light blue, Turquoise leaves white; luster reads dull on Sieleckiite and waxy on Turquoise.
How to tell apart: Streak differs — Sieleckiite leaves light blue, Variscite leaves white; luster reads dull on Sieleckiite and waxy on Variscite.
How to tell apart: Streak differs — Sieleckiite leaves light blue, Wavellite leaves white; luster reads dull on Sieleckiite and vitreous on Wavellite.
Often found alongside sieleckiite
Minerals reported to co-occur with sieleckiite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₃Al₄(PO₄)₂(OH)₁₂·2H₂O
- Mohs hardness
- 3
- Density
- 3.37 g/cm³
- Colors
- Streak
- Light Blue
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Triclinic
- Crystal habit
- Fibrous, Spherical, Botryoidal Crusts
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Hydrothermal Copper-gold Deposits
- Typical price
- $50-500 depending on specimen size and quality
Where rockhounds find sieleckiite
Classic worldwide localities
- Capillitas Mine, Argentina
Field-hunting tip
Look in oxidized hydrothermal copper-gold deposits country — that is the host setting where sieleckiite typically forms. If you start seeing malachite, chrysocolla, goethite in float, you are in the right ground. Field specimens usually show a fibrous, spherical, botryoidal crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find sieleckiite on the map
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