Plumboagardite
Chemical formula: (Pb²⁺,REE,Ca)Cu²⁺₆(As⁵⁺O₄)₃(OH)₆·3H₂O
Plumboagardite is a rare lead-copper arsenate, forming characteristic acicular crystals of an intense blue-green color.
Properties
- Mohs hardness
- 3
- Color
- Green, pale greenish
- Luster
- Vitreous to silky
- Streak
- Greenish
- Density
- 0
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Hexagonal
Diagnostic features
## Identification The key diagnostic feature of plumboagardite is its fine, acicular or hair-like crystals gathered in radial aggregates with a characteristic blue-green or yellowish-green color. It occurs in the oxidation zones of copper and lead ores. ## Distinguishing from similar minerals Plumboagardite is visually almost impossible to distinguish from other minerals of the mixite group (e.g., agardite-(Y), agardite-(Ce), mixite) without advanced chemical analysis (EDS/WDS) to determine the dominant rare earth element or lead. It can be confused with other secondary copper minerals, such as malachite (reacts with acid), brochantite, or olivenite, but the crystal form of plumboagardite is usually more delicate and acicular. ## Crystal forms Crystals are hexagonal, very elongated along the c-axis, forming acicular and hair-like shapes. They usually occur as radial or stellate aggregates, as well as tangled masses resembling felt or glass wool.
Geological environment
## Genesis Plumboagardite is a secondary mineral, forming in the oxidation (weathering) zones of polymetallic ore deposits rich in arsenic, copper, and lead. It forms as a result of surface waters acting on primary ore minerals. ## Mineral associations It often co-occurs with other secondary arsenate and sulfate minerals. Typical associated minerals include malachite, cerussite, mimetite, olivenite, bayldonite, duftite, anglesite, goethite, and quartz. ## Localities Important localities worldwide, from which well-formed specimens originate, include the Clara mine in the Black Forest (Germany), Laurion (Greece), Tsumeb (Namibia), Bou Skour (Morocco), and some mines in Arizona and Utah (USA).
Rarity
Rare
For collectors
## Quality criteria The most valued specimens by collectors are those with well-defined, radial aggregates of intense, vibrant color. The contrast with the rock matrix on which the crystals occur significantly enhances visual appeal. The size of the aggregates and the absence of damage to the delicate needles are also important. Specimens with well-documented localities are more highly valued. ## Popular localities Specimens from Greek Laurion are classics and highly regarded. Very aesthetic, yellowish-green aggregates come from the Bou Skour mine in Morocco. The Clara mine in Germany, being the type locality, has also provided many high-quality specimens.
Care and storage
## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to the fragility and delicacy of the acicular crystals, wet or mechanical cleaning is not recommended. If absolutely necessary, distilled water and compressed air can be used for drying. ## What to avoid Avoid contact with all chemicals, especially acids, which can damage the mineral. Fragile crystals are sensitive to ultrasound, vibrations, and impacts. Protect it from high temperatures and sudden temperature changes. ## Storage It is recommended to store specimens in closed, padded boxes or display cases to protect them from dust, mechanical damage, and direct contact. Avoid placing heavier minerals nearby, which could crush the delicate needles.