Pradetite
Chemical formula: Co²⁺Cu²⁺₄(As⁵⁺O₄)₂(As⁵⁺O₃OH)₂·9H₂O
Pradetite is a very rare, hydrated cobalt and copper arsenate, forming microscopic, blue-green, platy crystals.
Properties
- Mohs hardness
- 3
- Color
- Green
- Luster
- Vitreous
- Streak
- White
- Density
- 3.33
- Cleavage
- Perfect on {010}
- Fracture
- Conchoidal
- Transparency
- Transparent
- Crystal system
- Triclinic
Diagnostic features
## Identification Identification of pradetite is possible almost exclusively using advanced analytical methods, such as Raman spectroscopy or chemical analysis by electron microprobe (EDS/WDS). Preliminary identification in a collection is based on its characteristic blue-green color, platy habit of microcrystals, and co-occurrence with other rare arsenates from the Cap Garonne mine. ## Distinguishing from Similar Minerals It can be confused with many other secondary blue or green copper minerals, especially other arsenates. It is distinguished from geminite by the presence of cobalt. It differs from cyanotrichite by its crystal habit (platy instead of acicular). Certain differentiation requires chemical analysis. ## Crystal Forms Pradetite forms very small, thin, platy crystals with a lamellar habit, elongated in one direction. These crystals often combine into radial or rosette-like aggregates, and also form thin coatings on the host rock.
Geological environment
## Genesis Pradetite is a secondary mineral, formed in the oxidation zones (gossans) of polymetallic deposits rich in arsenic. It forms as a result of the weathering of primary sulfides and arsenides, especially tennantite, in the presence of copper and cobalt-rich solutions. It forms under low temperature and pressure conditions. ## Mineral Associations This mineral co-occurs with other rare arsenates, particularly at its type locality. It is most commonly associated with: geminite, olivenite, tennantite, chalcopyrite, covellite, barite, quartz, as well as newly described or rare minerals such as capgaronnite or pushcharovskite. ## Localities The only confirmed and well-documented occurrence of pradetite in the world is its type locality - the Cap Garonne mine in Le Pradet, Var department, France. This is a historic copper and lead mine, known for its exceptional mineralogy of secondary arsenates.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of pradetite specimens is assessed primarily based on the abundance and visibility of crystals on the rock matrix. The most valued specimens are those with clearly formed, though still microscopic, rosette-like aggregates of intense, blue-green color. Contrast with the substrate and the presence of rare associated minerals are also important. ## Popular Localities The only source of pradetite specimens is the Cap Garonne mine in France. Material from this locality is highly prized by collectors specializing in rare minerals and "micromounts."
Care and storage
## Cleaning Pradetite specimens should not be cleaned mechanically or chemically. Any attempts at cleaning may irreversibly damage the microscopic crystals. If absolutely necessary, compressed air can be used from a safe distance to remove dust. ## What to Avoid Avoid contact with water, acids, bases, and any solvents. As an arsenate, it is chemically sensitive. Protect it from high temperatures, which can lead to dehydration and structural changes. Avoid vibrations and impacts. ## Storage Specimens should be stored in stable conditions, in a closed, padded "micromount" box, to protect them from mechanical damage, dust, and humidity changes. Do not expose it to direct sunlight.