Skippenite
Chemical formula: Bi<sup>3+</sup><sub>2</sub>Se<sup>2-</sup><sub>2</sub>Te<sup>2-</sup>
Skippenite is a very rare bismuth seleno-telluride, forming small, platy crystals with a metallic luster.
Properties
- Mohs hardness
- 2
- Luster
- Metallic
- Streak
- Black
- Density
- 8.05
- Cleavage
- Perfect on {0001}
- Fracture
- Micaceous
- Transparency
- Opaque
- Crystal system
- Trigonal
Diagnostic features
## Identification Amateur identification of skippenite is practically impossible due to its small size and resemblance to many other bismuth sulfides and tellurides. Identification requires advanced analytical methods, such as electron microprobe analysis (EDS/WDS) to confirm the chemical composition (presence of bismuth, selenium, and tellurium in appropriate proportions) and X-ray diffraction (XRD) to determine the crystal structure. ## Distinguishing from Similar Minerals Skippenite is visually indistinguishable from many other rare bismuth minerals, such as kawazulite, tellurobismuthite, tsumoite, or poubaite. All form small, silvery, metallic flakes. Definitive differentiation is possible only through precise chemical analysis. ## Crystal Forms This mineral forms very small, thin, platy crystals with a hexagonal outline. It also occurs as lamellar or granular aggregates, most often as inclusions in other minerals.
Geological environment
## Genesis Skippenite is a hydrothermal mineral. It forms in the final stages of crystallization in quartz-carbonate veins associated with uranium deposits. It crystallizes under low-temperature conditions from solutions rich in bismuth, selenium, and tellurium. ## Mineral Associations At the type locality (Otish mine, Canada), skippenite co-occurs with quartz, dolomite, uraninite, fluorite, as well as other rare bismuth tellurides and selenides, such as kawazulite, tsumoite, and poubaite. It often occurs as inclusions in kawazulite or in its close vicinity. ## Localities Skippenite is an extremely rare mineral, confirmed in only a few locations worldwide. The most important of these are: - Type locality: Otish uranium mine, Otish Mountains, Quebec, Canada. - Boksitogorsk mine in the Southern Urals, Russia. - Kochbulak gold deposit in Uzbekistan. - Trixie Mine, East Tintic District, Utah, USA.
Rarity
Extremely rare
For collectors
## Quality Criteria Due to the extreme rarity and microscopic size of its crystals, the main criterion for value for collectors is the mere presence of analytically confirmed skippenite in a sample. Specimens in which skippenite forms identifiable, even if very small, standalone crystals or flakes on a rock matrix, rather than just microscopic inclusions, are most highly prized. Precise documentation and labeling, often with an accompanying chemical analysis result (EDS), are crucial. The richness of associations with other rare bismuth minerals also increases the specimen's value.
Care and storage
## Cleaning Skippenite specimens, due to their extreme rarity, small size, and softness, should generally not be mechanically cleaned. Any attempts can easily damage or destroy the delicate crystals. If absolutely necessary, compressed air (from a safe distance) can be used to remove loose dust particles. ## What to Avoid Contact with chemicals, acids, and ultrasonic cleaners must be strictly avoided. The mineral is very soft (Mohs hardness 2), so it should be protected from scratching by harder minerals. It should not be heated or exposed to sudden temperature changes. ## Storage Skippenite must be stored under stable conditions, preferably in a sealed "micromount" box, which protects it from dust, mechanical damage, and contact with other minerals. Moisture and direct sunlight should be avoided, although its light sensitivity is not known.