Raberite
Chemical formula: Tl<sup>1+</sup><sub>5</sub>Ag<sup>1+</sup><sub>4</sub>As<sup>3+</sup><sub>6</sub>Sb<sup>3+</sup>S<sup>2-</sup><sub>15</sub>
Raberite is an extremely rare thallium, silver, arsenic, and antimony sulfosalt, found exclusively in the Swiss Binn Valley.
Description
## Characteristics Raberite is a black, opaque mineral with a metallic luster. It occurs as very small, irregular (anhedral) grains, not exceeding 200 micrometers in size. It is typically intergrown with other minerals, mainly sulfosalts, and does not form crystals visible to the naked eye. Due to its microscopic nature, its presence can only be confirmed using advanced analytical techniques. ## Physical Properties The luster of raberite is metallic, and the mineral itself is completely opaque. Its density, calculated based on its chemical composition and unit cell parameters, is 5.51 g/cm³. Hardness, cleavage, and fracture have not been determined due to the too small size of the grains, which prevents standard testing. ## Colors and Varieties This mineral has a uniform, black color. No color varieties or commercial varieties are known. ## History and Name The name raberite was given in honor of the Swiss mineralogist Thomas Raber, in recognition of his contribution to the study of minerals from the Lengenbach quarry. The mineral was officially approved by the International Mineralogical Association (IMA) in 2011. ## Applications Raberite has no industrial applications. Its significance is purely scientific and collectible, being an object of interest for specialized research institutions and collectors of microscopic minerals.
Diagnostic features
## Identification Identification of raberite is impossible based on visual characteristics. Due to its microscopic nature and appearance similar to many other sulfosalts, the only reliable method of identification is advanced chemical analysis, such as X-ray microanalysis (EDS/WDS). In practice, this means that this mineral can only be identified under laboratory conditions. ## Distinguishing from similar minerals Raberite is visually indistinguishable from numerous rare sulfosalts occurring in the same locality, such as hutchinsonite, imhofite, wallisite, or jentschite. All form small, black grains with a metallic luster. Reliable differentiation requires specialized research equipment. ## Crystal forms This mineral occurs exclusively in the form of anhedral (irregular, lacking their own faces) grains, usually ranging from a few to 200 micrometers in size. It does not form well-developed, macroscopic crystals.
Geological environment
## Genesis Raberite forms as a result of low-temperature hydrothermal processes. It crystallizes in vugs and fractures of saccharoidal dolomites from the Triassic period, which have been subjected to solutions rich in thallium, arsenic, antimony, and sulfur. ## Mineral associations This mineral occurs in close association with other rare sulfosalts typical of the Lengenbach deposit. It is most often found in association with realgar, hatchite, and jentschite. ## Localities The only confirmed locality of raberite in the world is the Lengenbach quarry in the Binn Valley (Binnatal) in the canton of Valais, Switzerland. This is its type locality.
Rarity
Extremely rare
Collector aspects
## Quality criteria For a microscopic mineral such as raberite, traditional quality criteria do not apply. The value of a specimen depends on laboratory confirmation of the mineral's presence, the abundance of its occurrence (number of grains on the rock matrix), and the quality of associated minerals, e.g., well-formed realgar crystals. The specimen is valuable primarily due to its extreme rarity and scientific significance. ## Popular localities All known raberite specimens come from a single location in the world – the Lengenbach quarry in Switzerland. This is the locality from which the most prized and only available materials for research and collections originate.
Care and storage
## Cleaning Due to the microscopic size of the grains and high toxicity, cleaning specimens containing raberite is strongly discouraged. Any attempt at mechanical or chemical cleaning may lead to the release of toxic dusts and damage to the delicate specimen. If absolutely necessary, a stream of compressed air or a very soft brush can be used, performing these actions with the utmost caution. ## What to avoid **WARNING: Highly toxic mineral.** Contains thallium and arsenic. Avoid any skin contact and inhalation of dust. Hands should be thoroughly washed after any potential contact. It must not be heated, subjected to acids, or mechanical processing (e.g., grinding), as this leads to the release of toxic substances. It should be protected from moisture. ## Storage Specimens containing raberite must be stored in a sealed, permanently closed, and clearly labeled container (e.g., a "perky box"). They should be kept away from other minerals to prevent contamination, and out of reach of children and pets.