Poubaite
Chemical formula: Pb<sup>2+</sup>Bi<sup>3+</sup><sub>2</sub>(Se<sup>2-</sup>,Te<sup>2-</sup>,S<sup>2-</sup>)<sub>4</sub>
Poubaite is a rare lead bismuth selenide, forming acicular crystals and coatings with a metallic luster.
Properties
- Luster
- Metallic
- Streak
- Black
- Density
- 8.36
- Cleavage
- Perfect on {001}
- Transparency
- Opaque
- Crystal system
- Tetragonal
Diagnostic features
## Identification Poubaite is identified by its characteristic form – very fine, acicular or hair-like crystals forming aggregates and coatings. Key features include its steel-gray to black color, strong metallic luster, and occurrence in a specific geological environment, such as hydrothermal veins. Final identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Poubaite can be confused with other acicular sulfosalts or selenides, such as jamesonite, boulangerite, clausthalite, or guanajuatite. Differentiation with the naked eye is practically impossible. Key factors are its association with other bismuth and lead selenides and chemical analysis confirming the presence of lead, bismuth, and selenium as main components. ## Crystal Forms The mineral forms elongated, acicular or hair-like crystals, often with a square cross-section. These crystals grow in radial aggregates, tangled felt-like masses, or as individual needles grown on other minerals, mainly calcite.
Geological environment
## Genesis Poubaite is a mineral of hydrothermal origin. It forms in ore veins, crystallizing at relatively low temperatures from solutions rich in lead, bismuth, and selenium. In its type locality (Předbořice), it is associated with calcite-uraninite veins cutting amphibolite rocks. ## Mineral Associations This mineral co-occurs with other selenides and sulfides. In Předbořice, it was found in association with clausthalite, berzelianite, umangite, eskebornite, tiemannite, chameanite, klockmannite, uraninite, pyrite, chalcopyrite, and hematite. The main gangue mineral is calcite. ## Localities The most important and type locality, from which the best-formed specimens originate, is Předbořice near Klatovy in the Czech Republic. Other confirmed occurrences include the Tumiñico mine in Sierra de Cacho, Argentina, and the Zálesí vein in the Jawornik region, Czech Republic. It is an extremely rare mineral.
Rarity
Very rare
For collectors
## Quality Criteria The collector's appeal of poubaite primarily depends on the richness and aesthetics of the acicular crystal aggregates. Most valued are specimens showing dense, but undamaged, "plush" coatings or radial aggregates on a contrasting matrix, most often white calcite. The size of the crystals, although always small, is also important – the longer and better-defined the needles, the more valuable the specimen. A confirmed locality, especially Předbořice, is also important. ## Popular Localities By far the most classic and sought-after locality by collectors is the type locality – Předbořice in the Czech Republic. Specimens from this location are considered exemplary for this mineral.
Care and storage
## Cleaning Poubaite specimens are extremely delicate due to the fine, acicular form of the crystals. Mechanical cleaning is highly inadvisable. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust. Avoid contact with water and any chemicals. ## What to Avoid Avoid ultrasonics, steam cleaners, acids, solvents, and detergents. The crystals are very brittle and fragile, so the specimen should be protected from shocks, impacts, and abrasions. As a selenide, the mineral may be sensitive to chemical changes in reaction with moisture and oxygen from the air. ## Storage Specimens should be stored exclusively in sealed collector boxes that protect them from dust, mechanical damage, and sudden changes in humidity. Due to the presence of lead, it is recommended to wash hands after handling the mineral.