Aleksite
Chemical formula: Pb<sup>2+</sup>Bi<sup>3+</sup><sub>2</sub>Te<sup>2-</sup><sub>2</sub>S<sup>2-</sup><sub>2</sub>
Aleksite is a very rare mineral from the sulfotelluride group, being a lead and bismuth telluride and sulfide, forming lamellae with a metallic luster.
Properties
- Mohs hardness
- 2.5
- Luster
- Metallic
- Streak
- Black
- Density
- 7.8-8.0
- Cleavage
- Perfect on {0001}
- Fracture
- Flexible
- Transparency
- Opaque
- Crystal system
- Trigonal
Diagnostic features
## Identification Characteristic features of aleksite include its steel-gray color, strong metallic luster, very low hardness (2.5 on the Mohs scale), and perfect cleavage, manifested by its tendency to split into thin lamellae. It is also very dense. Its occurrence in association with gold and other tellurides in quartz veins is an important clue. ## Distinguishing from Similar Minerals Macroscopic differentiation of aleksite from other rare bismuth tellurides and sulfosalts (e.g., tetradymite, joseite, pilsenite) is practically impossible without advanced laboratory analysis. All these minerals have very similar appearance, hardness, and habit. Certain identification requires chemical analysis (EDS) or X-ray diffraction (XRD). ## Crystal Forms Aleksite forms lamellar, scaly, and platy aggregates. It occurs as thin, flexible lamellae of irregular shapes or as imperfect tabular crystals with a hexagonal outline, reaching sizes up to several millimeters.
Geological environment
## Genesis Aleksite is a hydrothermal mineral. It forms in quartz-gold veins, which develop under low to medium temperature conditions. ## Mineral Associations It most commonly co-occurs with native gold, bismuth, galena, and pyrite. It is also accompanied by other rare tellurides, such as tetradymite, altaite, petzite, hessite, calaverite, and rickardite. ## Localities This is a very rare mineral, known from a few localities worldwide. The most important ones include: - Alekseevskoe mine on the Aldan Plateau in Yakutia (Russia) - type locality. - Robb-Montbray and Mattagami Lake mines in the Abitibi region, Quebec (Canada). - Trixie mine in the East Tintic district, Utah (USA).
Rarity
Very rare
For collectors
## Quality Criteria The quality of aleksite specimens is assessed primarily based on its presence and identifiability, rather than aesthetic value. Microcrystals or well-formed lamellae are most prized, especially if they occur in association with gold or other well-defined, rare tellurides. Due to the nature of the mineral, specimens are usually small (millimeter-sized) and intended for collectors specializing in rare minerals and systematics. ## Popular Localities The most well-known specimens, though still extremely rare on the collector's market, come from the Canadian province of Quebec (Robb-Montbray and Mattagami Lake mines). Material from the Russian type locality is practically unavailable.
Care and storage
## Cleaning Aleksite specimens are extremely delicate and should be handled with the utmost care. Only a soft brush or a stream of compressed air from a safe distance should be used to remove dust. Absolutely avoid contact with water, ultrasonic cleaners, and any chemical agents. ## What to Avoid The mineral is very soft and has perfect cleavage, making it susceptible to scratches, dents, and delamination even under slight pressure. It should be protected from moisture, which can accelerate oxidation processes and tarnish formation. Avoid sudden temperature changes. ## Storage It is recommended to store aleksite specimens in separate, padded "micromount" boxes to prevent contact with other minerals and mechanical damage. Display should be in a closed cabinet, under stable humidity conditions, and away from direct sunlight.