Fuettererite
Chemical formula: Pb<sup>2+</sup><sub>3</sub>Cu<sup>2+</sup><sub>6</sub>Te<sup>6+</sup>O<sub>6</sub>(OH)<sub>7</sub>Cl<sub>5</sub>
Fuettererite is a very rare oxychloride of lead, copper, and tellurium, forming small, tabular crystals of an intense green color.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous to greasy
- Streak
- Light green
- Density
- 5.13
- Cleavage
- Perfect on {0001}
- Fracture
- Brittle
- Transparency
- Transparent to translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification Identifying fuettererite under collector conditions is practically impossible without specialized equipment. It relies on a unique combination of features: its occurrence as small, hexagonal, tabular crystals of an emerald-green color, a light green streak, and its co-occurrence with other rare tellurates and chlorides in the only known locality. ## Distinguishing from Similar Minerals It can be confused with other green secondary copper minerals, such as brochantite, malachite, or other rare tellurates. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS), due to its unique chemical composition (presence of Pb, Cu, and Te). ## Crystal Forms Fuettererite forms thin, tabular crystals with a hexagonal outline. These crystals often combine into small, rosette-like or irregular aggregates.
Geological environment
## Genesis Fuettererite is a secondary mineral that forms in the oxidation zone of low-temperature, polymetallic hydrothermal deposits. Its formation is a result of the weathering processes of primary ore minerals in the presence of tellurium, copper, lead, and chlorine under alkaline and strongly oxidizing conditions. ## Mineral Associations This mineral occurs in association with other rare secondary minerals. In its type locality, it was found in association with anglesite, baryte, chlorargyrite, cuproadamite, mimetite, wulfenite, and other rare tellurates, such as dugganite, jensenite, and ottoite. ## Localities The only confirmed locality for fuettererite in the world is the Otto Mountain mine, located in San Bernardino County, California, USA. This is its type locality.
Rarity
Extremely rare
For collectors
## Quality Criteria As a "micromount" type mineral, the value of a specimen is primarily determined by the quality and size of the crystals, even though they are always very small. The most desirable specimens are those with sharply defined, undamaged, tabular crystals forming aesthetic, rosette-like aggregates. The intensity of the emerald-green color and the richness of its association with other rare minerals also significantly increase its collector and scientific value. ## Popular Localities The only source of fuettererite specimens is its type locality – the Otto Mountain mine in California, USA. All specimens available on the collector market originate from this single location.
Care and storage
## Cleaning Due to the extreme rarity and fragility of specimens, no mechanical or chemical cleaning is recommended. Any contaminants, such as dust, should be removed very carefully, preferably with a photographic blower. Contact with water is inadvisable. ## What to Avoid Avoid contact with all chemicals, acids, detergents, and water. Specimens are very brittle and sensitive to mechanical damage, vibrations, and temperature changes. They should not be exposed to direct sunlight. ## Storage Fuettererite specimens should be stored exclusively in specialized, sealed "micromount" boxes, protecting them from dust, moisture, and physical damage. They should be kept in stable room conditions, away from heat and light sources.