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.
Description
## Characteristics Aleksite is a mineral belonging to the sulfotelluride group. It usually occurs as small, thin plates, lamellae, or scales, forming granular and lamellar aggregates. Imperfect, tabular crystals with a hexagonal outline are rarely observed. Its appearance is typical for many bismuth tellurides—it has a steel-gray to tin-white color and a strong, metallic luster. Sometimes a dull, yellowish tarnish appears on its surface. ## Physical Properties This mineral is very soft; its Mohs hardness is 2.5, which means it can be scratched with a fingernail. It is opaque and has a high density, ranging from 7.8 to 8.0 g/cm³. It possesses perfect cleavage in one plane, causing it to easily separate into thin, flexible lamellae. ## Colors and Varieties The primary color of aleksite is steel-gray, transitioning to tin-white. Some specimens may be covered with a yellowish weathering tarnish. No color or commercial varieties are distinguished. ## History and Name Aleksite was first described in 1978 by a group of Russian mineralogists (V. A. Kovalenker, V. L. Rusinov, N. V. Troneva, E. N. Zav'yalov). The mineral is named in honor of Anatoliy Ivanovich Alekseev (1929-1997), a Russian geologist who discovered the Alekseevskoe gold deposit on the Aldan Plateau in Russia, where this mineral was first identified. ## Applications Due to its extreme rarity, aleksite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced systematic collections.
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
Collector aspects
## 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.