Paddlewheelite
Chemical formula: MgCa₅Cu²⁺₂(U⁶⁺O₂)₄(CO₃)₁₂(H₂O)₃₃
Paddlewheelite is a very rare uranyl mineral, distinguished by its unique crystal structure resembling paddlewheels and an intense blue-green color.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous
- Streak
- Pale blue green
- Density
- 2.497
- Cleavage
- {100}
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Diagnostic features of paddlewheelite include its unique form as spherical aggregates resembling paddlewheels, intense blue-green color, and very low hardness. The mineral also exhibits strong radioactivity, easily detectable with a Geiger counter. The streak has a characteristic pale greenish-blue color. ## Distinguishing from similar minerals Due to its exceptional morphology, paddlewheelite is difficult to confuse with other minerals. Other secondary copper and uranium minerals (e.g., some varieties of uranophane, cuprosklodowskite) may have a similar color, but none of them form such characteristic, radial "paddlewheel" aggregates. ## Crystal forms Paddlewheelite forms spherical or hemispherical aggregates up to 0.3 mm in diameter. These aggregates are composed of extremely thin, tabular crystals with a rhombic outline, which radiate outwards from a common center. This specific structure is the most characteristic visual feature of the mineral.
Geological environment
## Genesis Paddlewheelite is a secondary uranium mineral that crystallizes in the oxidation zones of ore deposits containing uraninite. It forms as a result of the action of solutions rich in carbonates, copper, calcium, and magnesium on primary uranium ores. Its presence indicates specific chemical conditions prevailing within the deposit. ## Mineral associations At its type locality, paddlewheelite occurs in association with other rare secondary minerals. Its co-occurrence has been noted with andersonite, liebigite, schröckingerite, bayleyite, as well as with gypsum and probably other, yet unidentified mineral phases. ## Localities The only confirmed occurrence of paddlewheelite in the world is its type locality – the Klement vein in the historic Svornost mine in Jáchymov (formerly Sankt Joachimsthal), Czech Republic. This is one of the world's most important sites for secondary uranium minerals.
Rarity
Extremely rare
For collectors
## Quality criteria The quality of a paddlewheelite specimen is primarily assessed based on the development and clarity of its unique aggregates. Most valued are micromounts where well-defined, isolated "paddlewheels" with an intense, blue-green color are visible. The aesthetics of the rock matrix and the presence of associated minerals, which enhance the scientific and visual value of the specimen, are also important. Due to its microscopic size, the quality of the photomicrography is crucial. ## Popular localities The only source of paddlewheelite specimens is its type locality in Jáchymov, Czech Republic. All specimens available on the collector's market originate from this single location, making them extremely desirable for specialized collectors of rare and uranium minerals.
Care and storage
## Cleaning The mineral is extremely delicate and fragile. Mechanical cleaning is inadvisable and risks destroying the specimen. No liquids or ultrasonics should be used. Any contaminants, such as dust, can only be removed very carefully with a soft brush or a photographic air blower. ## What to avoid Paddlewheelite is a very sensitive mineral. Contact with water and chemicals must be strictly avoided. As a secondary mineral, it is unstable under fluctuating humidity conditions. Due to its uranium content, it is highly radioactive, which requires appropriate safety precautions – direct skin contact should be avoided, dust should not be inhaled, and hands should be washed after any contact. ## Storage Paddlewheelite specimens must be stored under specialized conditions. It is best to place them in a sealed, closable container (e.g., a "membrane box") that protects against mechanical damage and humidity changes. Due to radioactivity, it should be stored away from areas of permanent human presence, in a marked container, preferably in a lead shield to limit radiation.