Aschamalmite
Chemical formula: Pb<sup>2+</sup><sub>6-3x</sub>Bi<sup>3+</sup><sub>2+x</sub>S<sup>2-</sup><sub>9</sub>
Aschamalmite is a rare lead bismuth sulfide, forming acicular crystals with a metallic luster, found in Austria.
Properties
- Luster
- Metallic
- Streak
- Black
- Cleavage
- Good on {100}
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Aschamalmite is primarily identified by its characteristic form – very thin, elongated, often tangled crystals with a metallic luster. Its steel-gray color and occurrence in a specific geological environment are also key indicators. ## Differentiation from similar minerals It can be confused with other acicular sulfides, such as jamesonite, boulangerite, or aikinite. Final differentiation requires advanced analytical methods, such as chemical analysis (EDS) or X-ray diffraction (XRD), due to the visual similarity to many other "feather ores." ## Crystal forms It exclusively forms acicular or hair-like crystals, elongated along the [010] axis. These crystals often occur as tangled or radial aggregates, growing on other minerals, mainly quartz.
Geological environment
## Genesis Aschamalmite is a hydrothermal mineral. It forms in Alpine fissure-type veins that cut through gneisses and amphibolite schists. It crystallizes in the late stages of hydrothermal processes at relatively low temperatures. ## Mineral associations It most commonly co-occurs with quartz, which forms the host rock for its crystals. In its type locality, it is also accompanied by other sulfides and sulfosalts, such as galena, chalcopyrite, sphalerite, aikinite, beryllinite, cosalite, friedrichite, hammarite, krupkaite, lindstromite, paderite, and rezbanyite, as well as hematite and chlorite. ## Localities The only confirmed and thoroughly described occurrence of aschamalmite in the world is its type locality – the Ascham Alm deposit, located in the Untersulzbach valley, in the state of Salzburg, Austria.
Rarity
Very rare
For collectors
## Quality criteria The most valuable aschamalmite specimens are those with dense, undamaged clusters of long, shiny needles, clearly contrasting against a light background, most often milky quartz. Color contrast and the aesthetic arrangement of crystals significantly increase collector value. Due to its rarity, even microscopic but well-formed crystals are prized. ## Popular localities The only source of collector specimens is the historical type locality in Ascham Alm, Austria. Material from this location is extremely difficult to acquire and appears on the market very rarely, mainly from historical collections.
Care and storage
## Cleaning Due to the extreme delicacy of the acicular crystals, mechanical cleaning is not recommended. Any attempts to use brushes, even soft ones, can damage the specimen. If cleaning is absolutely necessary, compressed air can be carefully used from a safe distance to remove loose dust. ## What to avoid Avoid contact with chemicals, acids, and detergents. The mineral is sensitive to shocks and vibrations, which can cause the fragile crystals to break. It should not be heated or exposed to sudden temperature changes. ## Storage Aschamalmite specimens require storage in stable conditions, preferably in a sealed "membrane box" or a padded collector's box that protects against dust and mechanical damage. It should be kept away from sources of vibration.