Sieleckiite
Chemical formula: Cu<sup>2+</sup><sub>3</sub>Al<sub>4</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>12</sub>·2H<sub>2</sub>O
Sieleckite is a very rare, secondary copper and aluminum mineral, forming blue-green, rosette-like aggregates of microscopic crystals.
Properties
- Mohs hardness
- 2-3
- Luster
- Vitreous, Pearly
- Streak
- Light blue
- Density
- 3.25
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification Sieleckite is identified by its characteristic blue-green color, its occurrence in the form of small, spherical or rosette-like aggregates, and its specific, vitreous-pearly luster. Its origin is also key – it occurs in paragenesis with other secondary copper and arsenic minerals. ## Distinguishing from Similar Minerals It can be confused with other secondary copper phosphates and arsenates, such as turquoise, wavellite, pseudomalachite, or cyanotrichite. It differs from turquoise and wavellite by its more intense hue and specific mineral association. It differs from cyanotrichite by its crystal habit – sieleckite forms bladed aggregates, while cyanotrichite forms acicular ones. Final differentiation from very similar minerals, such as planerite, requires advanced chemical (EDS) or X-ray (XRD) analyses. ## Crystal Forms Sieleckite crystals are tabular or bladed, elongated along the [100] axis and flattened parallel to {010}. They typically form fan-shaped, rosette-like, or spherulitic aggregates up to 0.5 mm in diameter.
Geological environment
## Genesis Sieleckite is a secondary mineral, formed in the oxidation (weathering) zone of polymetallic deposits rich in copper and arsenic. It forms as a result of reactions between phosphate-rich solutions (likely originating from apatite decomposition) and copper and arsenic ore minerals in the presence of aluminum derived from gangue rocks (e.g., clay shales). ## Mineral Associations This mineral co-occurs with other secondary minerals such as malachite, azurite, chalcopyrite, tennantite, tyrolite, chalcophyllite, olivenite, cornetite, pseudomalachite, libethenite, goethite, quartz, and clay minerals. ## Localities The most important and type locality (localitas typica) for sieleckite is the historic "Miedzianka" mine near Jelenia Góra in Lower Silesia, Poland. This is the only confirmed and well-documented locality for this mineral worldwide.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of sieleckite specimens is primarily assessed based on the richness and aesthetics of the aggregates on the rock matrix. Samples with numerous, well-formed, intensely colored spherulites or rosettes, contrasting with the substrate, are most valued. The size of the aggregates, although always microscopic, is also important – larger (up to 0.5 mm) and more distinct clusters are rated higher. The presence of rare associated minerals is also significant. ## Popular Localities The only source of collector specimens is the type locality – the dumps and old workings of the "Miedzianka" mine in Poland. Material from this location is extremely rare and sought after by specialized systematic mineral and micromount collectors.
Care and storage
## Cleaning Sieleckite specimens are extremely delicate and fragile. Cleaning should be limited to an absolute minimum. If necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and any chemical agents. ## What to Avoid Absolutely avoid ultrasonic cleaners, mechanical cleaning (e.g., with brushes), contact with acids, detergents, and solvents. The mineral is sensitive to high temperatures and direct sunlight, which can cause fading or dehydration. ## Storage Specimens should be stored in stable conditions, in closed, padded "micromount" boxes to protect them from mechanical damage, dust, and sudden changes in humidity. Due to its fragility, it is not suitable for display outside of specialized containers.