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. Streak: pale blue.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: sky blue, royal blue.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fibrous, radial, spherical.
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, so Sieleckiite leaves pale blue, Turquoise leaves white to pale greenish blue; luster reads pearly on Sieleckiite and vitreous in crystals; dull to waxy if massive on Turquoise.
How to tell apart: Variscite is the harder of the two (Mohs 4.5 vs. ~3); streak differs, so Sieleckiite leaves pale blue, Variscite leaves white; luster reads pearly on Sieleckiite and vitreous to waxy on Variscite.
How to tell apart: Streak differs, so Sieleckiite leaves pale blue, Wavellite leaves white; luster reads pearly on Sieleckiite and vitreous to resinous, pearly 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
- 3.02 g/cm³
- Colors
- Sky blueRoyal blue
- Streak
- Pale blue
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Fibrous, radial, spherical
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral found in a fracture in a boulder from the oxidized zone of a copper deposit
Where rockhounds find sieleckiite
Classic worldwide localities
- Mt. Oxide copper mine, 150 km north of Mt. Isa, Queensland, Australia
Field-hunting tip
Where it forms: A rare secondary mineral found in a fracture in a boulder from the oxidized zone of a copper deposit. If you start seeing variscite, turquoise, libethenite in float, you are in the right ground. Typical habit: fibrous, radial, spherical. 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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