Stibioústalečite
Chemical formula: Cu¹⁺₆Cu¹⁺₆(Sb³⁺₂Te⁴⁺₂)Se²⁻₁₃
Stibioústalečite is a very rare copper, antimony, and tellurium selenide, distinguished by its complex chemical composition and occurrence as microscopic grains.
Properties
- Mohs hardness
- 3.5-4
- Luster
- Metallic
- Streak
- grey
- Density
- 5.676
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Opaque
- Crystal system
- Isometric
Diagnostic features
## Identification Identification of stibioústalečite is impossible without advanced laboratory techniques, such as chemical composition analysis (EDS) using a scanning electron microscope (SEM) and X-ray diffraction (XRD). For collectors, identification relies solely on a label from an analytically confirmed locality. ## Distinguishing from Similar Minerals This mineral can be confused with many other microscopic sulfides, selenides, and tellurides with a gray color and metallic luster, such as hakite, tetrahedrite, or ústalečite itself. Definitive differentiation requires specialized chemical analysis to reveal the unique proportion of copper, antimony, tellurium, and selenium. ## Crystal Forms Stibioústalečite occurs exclusively as anhedral (irregular, lacking crystal faces) grains and aggregates, usually as inclusions in other minerals.
Geological environment
## Genesis Stibioústalečite forms under hydrothermal conditions in calcite-uraninite veins. Its presence is associated with mineralization processes where solutions rich in selenium, antimony, tellurium, and copper crystallize in rock fractures. ## Mineral Associations This mineral coexists with uraninite (in which it forms inclusions), calcite, pyrite, chalcopyrite, bornite, digenite, covellite, clausthalite, berzelianite, umangite, bukovite, ústalečite, eskebornite, chameanite, and unspecified bismuth selenides. ## Localities The only confirmed occurrence of stibioústalečite in the world is its type locality: the Ústaleč uranium deposit, located near the town of Nalžovské Hory in the Plzeň Region of the Czech Republic.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a stibioústalečite specimen is determined not by the microscopic mineral itself, but by the richness of the mineral association on the matrix and the confirmation of its presence through analysis. Specimens where stibioústalečite coexists with other rare selenides are most desirable. The size of the grain itself, though always microscopic, is also important – larger grains are more valuable. ## Popular Localities The only source of specimens is the type locality in the Czech Republic. Material from this location is extremely difficult to obtain and appears on the collector's market sporadically, usually through specialized dealers and systematic mineral collectors.
Care and storage
## Cleaning Specimens containing stibioústalečite, due to the microscopic size of the grains and their occurrence as inclusions, practically do not require cleaning. If dust needs to be removed from the rock matrix, use a soft brush or compressed air from a safe distance. ## What to Avoid Avoid contact with chemicals, acids, and detergents, which could damage both the mineral itself and the surrounding matrix (e.g., calcite). Do not subject the specimen to ultrasonic cleaning or sudden temperature changes. ## Storage Specimens should be stored in stable conditions, away from moisture and direct sunlight. The safest method is to keep them in sealed "micromount" boxes, which protect against dust and mechanical damage.