Selenojunoite
Chemical formula: Cu<sup>1+</sup><sub>2</sub>Pb<sup>2+</sup><sub>3</sub>Bi<sup>3+</sup><sub>8</sub>Se<sup>2-</sup><sub>16</sub>
A very rare copper, lead, and bismuth selenide with a metallic luster, being the selenium analog of junoite.
Properties
- Mohs hardness
- 3.5-4
- Luster
- Metallic
- Streak
- Black
- Density
- 7.78
- Cleavage
- Good on {001}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Amateur identification of seleno-junoite is practically impossible. Preliminary identification is based on its metallic luster, high density, steel-gray color, and black streak. However, the analysis of paragenesis – co-occurrence with other rare selenides – is crucial. Definitive identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Seleno-junoite is visually indistinguishable from its sulfur analog, junoite. It can also be confused with many other selenides and sulfosalts with a similar appearance, such as clausthalite, galena, or lillianite. It differs from galena by being slightly harder and lacking perfect, three-directional cleavage. Final differentiation always requires laboratory testing. ## Crystal Forms It most commonly occurs as irregular grains and bladed or lamellar aggregates. It rarely forms elongated, prismatic crystals not exceeding a few millimeters in length, exhibiting striations on their faces.
Geological environment
## Genesis Seleno-junoite is a hydrothermal mineral. It forms under low-temperature conditions in ore veins rich in selenium, bismuth, and lead. ## Mineral Associations It most commonly co-occurs with other selenides, such as clausthalite, berzelianite, eskebornite, umangite, and klockmannite. It is also accompanied by uraninite, hematite, dolomite, and calcite. ## Localities This is a very rare mineral, known from only a few localities worldwide. The most important locality is the type locality – the Bytíz deposit near Příbram in the Czech Republic. Other confirmed occurrences include the El Dragón mine in the Potosí Department, Bolivia, and the Zálesí uranium deposit in the Czech Republic.
Rarity
Very rare
For collectors
## Quality Criteria The collector's value of seleno-junoite is primarily determined by the richness of the aggregates and the laboratory-confirmed identity of the mineral. Microscopic specimens are the norm. Those exhibiting even partially developed crystalline forms are exceptionally prized. Co-occurrence with other rare selenides on a single rock fragment also enhances its attractiveness. ## Popular Localities The most classic and sought-after specimens by collectors come from the type locality in the Czech Republic (Bytíz, Příbram). Specimens from the Bolivian El Dragón mine, known for its exceptional selenide mineralization, are also available on the market.
Care and storage
## Cleaning Seleno-junoite specimens are very sensitive to mechanical cleaning. Dust should be removed only with a soft brush or a stream of compressed air. Contact with water, especially tap water, is not recommended. If necessary, a small amount of distilled water can be used, and then the specimen should be thoroughly dried immediately. ## What to Avoid This mineral is sensitive to acids and other chemical reagents. Ultrasonic cleaners should be avoided, as they can damage delicate aggregates. It should be protected from moisture, which can accelerate oxidation and surface tarnishing processes. ## Storage It is recommended to store specimens in a dry and stable environment, preferably in sealed membrane boxes or display cases, which protect them from dust, moisture, and mechanical damage.