Zanelliite
Chemical formula: Pb²⁺Cu²⁺₉[As⁵⁺O₃.₅(OH)₀.₅]₂(As⁵⁺O₄)₂(OH)₉(H₂O)₃
Zanelliite is a very rare, turquoise-green lead-copper arsenate, forming microscopic, bladed crystals.
Properties
- Mohs hardness
- 3.5-0
- Luster
- Vitreous
- Streak
- pale green
- Density
- 4.425
- Cleavage
- {100}
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Characteristic features of zanelliite include its turquoise-green color, the formation of small, bladed crystals gathered in radial aggregates, and its occurrence in a specific geological environment. Final identification requires advanced analytical methods, such as chemical analysis (EDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Zanelliite can be confused with other secondary, green or blue copper minerals, such as aurichalcite, rosasite, or other rare arsenates. Distinguishing it based on visual characteristics is practically impossible and requires specialized studies. Association with the type locality and co-occurring minerals is key. ## Crystal Forms Zanelliite crystallizes in the form of very small, bladed or acicular crystals, which often arrange themselves into radial or stellate aggregates and rosettes. Single, well-formed crystals are extremely rare.
Geological environment
## Genesis Zanelliite is a secondary mineral, formed in the oxidation (weathering) zones of ore deposits. It forms in fissures and cavities of metamorphic rocks (e.g., quartzites), as a result of the alteration of primary minerals containing copper, lead, and arsenic. ## Mineral Associations This mineral co-occurs with other rare arsenates and secondary minerals. At the type locality, it was found in association with quartz, cafarsite, arsenosumeite, bayldonite, duftite, cornwallite, olivenite, agardite-(Y), as well as tennantite-(Zn) and chalcopyrite as primary minerals. ## Localities Zanelliite is an extremely rare mineral, known only from two adjacent localities in Switzerland, which constitute its type locality: Grosses Chalttal and Hochmättli in the Mürtschenalp region (Canton Glarus). These are the only confirmed occurrences of this mineral worldwide.
Rarity
Extremely rare
For collectors
## Quality Criteria As a "micromount" type mineral, the quality of a specimen is primarily determined by the richness and aesthetics of the crystal aggregates. Most valued are samples with distinct, well-formed rosettes or radial clusters of an intense, turquoise-green color. The size of these aggregates and their contrasting placement on the host rock (matrix) are also important. The purity of the specimen, i.e., the absence of damage to delicate crystals, is crucial. ## Popular Localities The only source of zanelliite specimens is its type locality in the Mürtschenalp region of Switzerland. All samples available on the collector's market originate from this single location.
Care and storage
## Cleaning Zanelliite specimens are extremely delicate and small. Mechanical cleaning is not recommended. If necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and any chemicals. ## What to Avoid The mineral should be protected from acids, detergents, and other chemical agents. As a relatively soft mineral, it is susceptible to scratches and mechanical damage. Avoid ultrasonic cleaning and sudden temperature changes. ## Storage It is recommended to store specimens in stable conditions, in closed "micromount" boxes, which protect them from dust, humidity, and physical damage. Display should be away from direct sunlight and heat sources.