Incomsartorite

Chemical formula: Tl₁+₆Pb₂+₁₄₄As₃+₂₄₆S₂-₅₁₆

Incomsartorite is a very rare, lead-gray sulfosalt of lead, arsenic, and thallium, forming acicular crystals in hydrothermal deposits.

## Characteristics Incomsartorite is a complex sulfosalt of lead, arsenic, and thallium. It forms elongated, acicular or capillary crystals, often tangled into felt-like aggregates. Individual crystals are flexible and pliable. The mineral has a metallic luster and a lead-gray color, sometimes with a dull, black tarnish. ## Physical Properties The mineral's luster is metallic. It is opaque. Due to its microcrystalline nature, precise determination of hardness and density is difficult; the density calculated from the formula and unit cell parameters is 5.82 g/cm³. ## Colors and Varieties Incomsartorite occurs in a lead-gray color. No varieties have been distinguished. ## History and Name The mineral's name comes from the Latin word *incompertus* (unknown, hidden) and the name of the mineral sartorite, referring to its complex, "hidden" crystallographic structure, which is a superstructure of sartorite. It was described as a new mineral in 2015 by a research team led by Dan Topa, after examining material from the Lengenbach quarry in Switzerland. ## Uses Incomsartorite has no industrial application. It is solely an object of scientific and collector interest due to its rarity and complex structure.

Properties

Luster: Metallic
Streak: Black
Density: 5.82
Cleavage: Good on {010}
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Incomsartorite is difficult to identify visually without specialized equipment. Characteristic features include clusters of very fine, flexible, acicular or capillary crystals with a metallic, lead-gray luster. It occurs in a specific geological environment – dolomites in the Lengenbach quarry. Certain identification requires advanced methods such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). ## Distinguishing from Similar Minerals It can be confused with many other lead and arsenic sulfosalts found in Lengenbach, such as sartorite, baumhauerite, rathite, or dufrénoyite, which form morphologically similar crystals. Visual distinction is practically impossible and requires laboratory analysis to determine chemical composition and crystal structure. ## Crystal Forms It forms very thin, elongated, acicular crystals, reaching up to 2 mm in length, but only a few micrometers thick. Crystals are often grouped into tangled, felt-like or woolly aggregates.

Geological environment

## Genesis Incomsartorite forms as a result of hydrothermal processes in veins cutting through dolomitic rocks. It is a product of crystallization from solutions rich in lead, arsenic, thallium, and sulfur at relatively low temperatures. ## Mineral Associations This mineral co-occurs with other lead and arsenic sulfosalts, such as sartorite, baumhauerite, rathite, dufrénoyite, as well as realgar, orpiment, and pyrite. It occurs directly on a dolomite matrix. ## Localities The only confirmed locality for incomsartorite 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 an incomsartorite specimen depends on the richness and aesthetics of the acicular crystal aggregates. Specimens with dense, but well-defined clusters on a contrasting, light dolomitic matrix are most valued. Association with other rare sulfosalts from Lengenbach is also important. ## Popular Localities The only source of specimens is the Lengenbach quarry in Switzerland. Collector material is extremely rare and available almost exclusively at specialized shows or through exchange among collectors specializing in minerals from this locality.

Care and storage

## Cleaning Incomsartorite specimens are extremely delicate. Mechanical cleaning should be avoided. If absolutely necessary, compressed air can be used from a safe distance to remove dust. Contact with water or other chemicals is not recommended. ## What to Avoid All chemicals should be avoided, especially acids, which can react violently with sulfosalts. The mineral is susceptible to mechanical damage – even touch can destroy the delicate, acicular crystals. It should be protected from high temperatures and humidity. ## Storage Specimens should be stored in sealed, padded "micromount" boxes to protect them from dust, humidity, and physical damage. Display should be in enclosed display cases, away from direct sunlight and sources of vibration.

Sources

IMA Mineral List (CNMNC)