Sicherite
Chemical formula: Tl<sup>1+</sup>Ag<sup>1+</sup><sub>2</sub>(As<sup>3+</sup>,Sb<sup>3+</sup>)<sub>3</sub>S<sup>2-</sup><sub>6</sub>
Sicherite is a very rare, black sulfosalt of thallium, silver, arsenic, and antimony, known exclusively from the Lengenbach quarry in Switzerland.
Description
## Characteristics Sicherite is a mineral with a metallic luster and black color. It occurs as very small, irregular (anhedral) grains, typically less than one millimeter in size. It most often forms small aggregates or is intergrown with other sulfosalts within the host rock. Due to its appearance and microscopic size, it is impossible to identify with the naked eye. ## Physical Properties This mineral is opaque and has a metallic luster. Its calculated density is approximately 6.13 g/cm³. Hardness has not yet been determined. No cleavage has been observed. ## Colors and Varieties Sicherite is uniform in its coloration – always black. No color varieties or commercial forms are known. ## History and Name The mineral's name, approved in 2000, honors Dr. Valentin Sicher (1926-2015), a Swiss mineral collector from Brig, who specialized in specimens from the Lengenbach quarry. This is the type locality (the only known) for sicherite. ## Applications Due to its extreme rarity and microscopic size, sicherite has no commercial or industrial applications. It is solely an object of scientific research and interest for specialized micromineral collectors.
Diagnostic features
## Identification Identification of sicherite is impossible without advanced laboratory techniques, such as X-ray microanalysis (EDS/WDS). Under collecting and field conditions, identification is unfeasible. The only reliable basis is chemical analysis confirming the presence and correct proportions of thallium, silver, arsenic, and antimony. ## Distinguishing from Similar Minerals Sicherite is visually indistinguishable from numerous black, metallic sulfosalts found in the Lengenbach quarry, such as hatchite, wallisite, rathite, or baumhauerite. The differences between them are purely chemical. ## Crystal Forms This mineral does not form well-developed, macroscopically visible crystals. It occurs exclusively as anhedral (irregular) grains and their small aggregates.
Geological environment
## Genesis Sicherite forms as a result of low-temperature hydrothermal processes. It crystallizes in voids and fissures within dolomites (so-called sugar dolomites) from solutions rich in thallium, silver, arsenic, antimony, and sulfur. ## Mineral Associations This mineral co-occurs with other rare sulfosalts typical of the Lengenbach deposit, primarily realgar, orpiment, hatchite, and wallisite. These minerals are accompanied by dolomite as the host rock. ## Localities The only confirmed locality for sicherite in the world is its type locality – the Lengenbach quarry in the Binn Valley (Binntal), Valais canton, Switzerland.
Rarity
Extremely rare
Collector aspects
## Quality Criteria The quality of a sicherite specimen is assessed based on several criteria. The most important is the certainty of identification confirmed by analysis. The richness of the occurrence (number of visible grains) and aesthetic associations with other minerals, e.g., contrast with red realgar, increase its value. The size of aggregates, even if measured in fractions of a millimeter, is also important for specialists. ## Popular Localities The most prized, and indeed the only, specimens come from the Lengenbach quarry in Switzerland. This is the classic and only known locality for this mineral.
Care and storage
## Cleaning Specimens containing sicherite should not be wet cleaned. Due to its toxicity, contact with the mineral should be kept to a minimum. Only gentle dust removal with a soft, dry brush, performed in a well-ventilated area, is permissible. ## What to Avoid **The mineral is highly toxic due to its thallium (Tl) and arsenic (As) content.** Inhaling dust must be strictly avoided. Hands should be thoroughly washed after any contact with the specimen. It must not be heated, crushed, or exposed to acids. It should be protected from moisture. ## Storage Specimens should be stored in a sealed, closed container (e.g., a "membrane box"), with a clear warning label about its toxicity. It is essential to keep it away from children, pets, and food. It is recommended to store it separately from other non-toxic minerals in the collection.