Schmiederite
Chemical formula: Cu<sup>2+</sup><sub>2</sub>Pb<sup>2+</sup><sub>2</sub>(Se<sup>4+</sup>O<sub>3</sub>)(Se<sup>6+</sup>O<sub>4</sub>)(OH)<sub>4</sub>
Schmiederite is a very rare lead and copper selenite-selenate mineral, forming small, prismatic, green crystals.
Properties
- Mohs hardness
- 3.5
- Luster
- Vitreous to Adamantine
- Streak
- Light green
- Density
- 6.36
- Cleavage
- Perfect on {100}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of schmiederite requires advanced analytical methods, such as Raman spectroscopy or chemical analysis using an electron microprobe (EDS/WDS), due to the microscopic size of the crystals. Visually, small, prismatic, green crystals in the oxidation zones of selenium deposits are characteristic. ## Distinguishing from Similar Minerals Schmiederite can be confused with other secondary copper and lead minerals, such as anglesite, linarite, or brochantite, and especially with other selenites and selenates (e.g., olsacherite, alvarezite). Definitive differentiation is only possible through chemical analysis confirming the presence of both selenium in two different oxidation states (Se⁴⁺ and Se⁶⁺), as well as lead and copper. ## Crystal Forms It forms elongated, prismatic crystals, often with pointed terminations. These crystals group into radial aggregates, rosettes, or tangled, felt-like clusters.
Geological environment
## Genesis Schmiederite is a secondary mineral, forming in the oxidation zones (gossans) of hydrothermal polymetallic deposits rich in selenium. It crystallizes as a result of the weathering of primary ore minerals containing copper, lead, and selenium under strongly oxidizing conditions. ## Mineral Associations This mineral co-occurs with other secondary selenium minerals, sulfates, and oxides. It is most commonly associated with: anglesite, olsacherite, alvarezite, chalcomenite, hematite, and goethite. ## Localities Schmiederite is an extremely rare mineral, known from only a few localities worldwide. The most important of these are: - Condor Mine, Sierra de Cacheuta, La Rioja Province, Argentina (type locality). - El Dragón Mine, Antonio Quijarro Province, Bolivia. - Baccu Locci Mine, Sardinia, Italy.
Rarity
Very rare
For collectors
## Quality Criteria The quality of schmiederite specimens is primarily assessed based on the richness and aesthetics of the microscopic crystals. The most desirable specimens are those with well-formed, undamaged crystals of intense green color, forming visually attractive aggregates on a contrasting rock matrix. Crystal size, although always small, is also important – larger needles are more valued. ## Popular Localities The best and most valued specimens come from the type locality in Argentina (Condor mine) and from the El Dragón mine in Bolivia, which has supplied a significant number of specimens of this mineral to the collector's market.
Care and storage
## Cleaning Due to its extreme rarity and delicacy, schmiederite specimens should generally not be cleaned. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and any chemicals. ## What to Avoid Avoid ultrasonic cleaners, chemicals, acids, and even water, which can damage delicate crystals or the host rock. The mineral is sensitive to shock and abrasion. ## Storage Specimens should be stored exclusively in specialized micromount boxes, protecting them from dust, shocks, and sudden changes in humidity. They should be kept in stable conditions, away from direct sunlight.