Wallisite
Chemical formula: Cu<sup>1+</sup>Pb<sup>2+</sup>Tl<sup>1+</sup>As<sup>3+</sup><sub>2</sub>S<sup>2-</sup><sub>5</sub>
Wallisite is a rare lead-copper-thallium sulfosalt with a metallic luster, found in dolomitic rocks in the Lengenbach quarry in Switzerland.
Properties
- Mohs hardness
- 3
- Luster
- Metallic
- Streak
- Reddish
- Density
- 5.86
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Triclinic
Diagnostic features
## Identification Amateur identification of wallisite is practically impossible. Identification requires advanced analytical methods, such as chemical composition analysis (EDS) and X-ray diffraction (XRD). A preliminary indication may be its occurrence in the specific geological environment of the Lengenbach quarry, in association with other rare sulfosalts. ## Distinguishing from Similar Minerals Wallisite is visually almost identical to many other rare, gray sulfosalts found in Lengenbach, such as hutchinsonite, imhofite, or hatchite. Definitive distinction is only possible through laboratory analysis. ## Crystal Forms This mineral forms very small, thin, tabular or bladed crystals, often grouped into small aggregates. Crystals rarely exceed 1-2 mm in size.
Geological environment
## Genesis Wallisite forms as a result of hydrothermal processes in metamorphic deposits. It occurs in dolomitic rocks (the so-called "Binn Dolomite") that have been subjected to solutions rich in sulfur, arsenic, thallium, and heavy metals. ## Mineral Associations This mineral co-occurs with other rare arsenic and thallium sulfosalts characteristic of the Lengenbach quarry. Its typical associated minerals include realgar, orpiment, hutchinsonite, hatchite, imhofite, lorandite, and pyrite. ## Localities The only confirmed and well-documented locality for wallisite in the world is the Lengenbach quarry in the Binn Valley (Binntal), in the canton of Valais, Switzerland. This is the type locality for this mineral.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a wallisite specimen is primarily determined by the quality and size of the crystals. Specimens with sharply defined, well-formed crystals are most valued, even if they are microscopic in size. Aesthetic composition with associated minerals is also important, for example, a contrasting combination with red realgar or yellow orpiment on white dolomite. Specimen purity and lack of damage are crucial. ## Popular Localities The only source of collectible specimens is the historic Lengenbach quarry in Switzerland. All legally obtained specimens come from this single location, making them highly desirable among collectors specializing in mineral systematics or minerals from this specific locality.
Care and storage
## Cleaning Wallisite specimens are extremely delicate and small. Cleaning, if absolutely necessary, should be limited to very careful dust removal using a soft brush or a photographic air blower. Avoid contact with water and any chemical agents. ## What to Avoid Absolutely avoid contact with chemicals, acids, and detergents. The mineral is sensitive to changes in temperature and humidity. It should not be heated or exposed to direct sunlight. Due to its arsenic, lead, and thallium content, it is toxic – avoid inhaling dust and wash hands after any contact. ## Storage Wallisite specimens should be stored under stable conditions, preferably in closed, padded "micromount" boxes that protect them from mechanical damage, dust, and sudden changes in humidity. Keep it away from children and pets, with clear labeling indicating its toxicity.