Argentodufrénoysite

Chemical formula: Ag₁+₃Pb₂+₂₆As₃+₃₅S₂-₈₀

Argentodufrénoysite is a rare, lead-gray sulfosalt mineral of silver, lead, and arsenic, forming fine, intergrown grains.

## Characteristics Argentodufrénoysite is a complex sulfosalt from the sartorite group, composed of silver, lead, arsenic, and sulfur. It occurs as very small, anhedral (not exhibiting its own crystal faces) grains, usually intergrown with other minerals, mainly sartorite. Its size rarely exceeds 100 micrometers. Visually, it is indistinguishable to the naked eye from other gray sulfosalts. ## Physical Properties The mineral is characterized by a metallic luster and a lead-gray color. Due to the microscopic size of the grains, most physical properties, such as hardness, density, or transparency, have not been precisely determined. The density calculated based on the chemical formula and unit cell parameters is 5.43 g/cm³. ## History and Name Argentodufrénoysite was first described in 2018 by a team of mineralogists led by Dan

Properties

Luster: Metallic
Streak: Black
Density: 5.43
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of argentodufrénoysite is possible only using advanced laboratory techniques, such as chemical analysis with an electron microprobe (EMPA) and X-ray diffraction (XRD). To the naked eye or under an optical microscope, it is practically indistinguishable from other lead sulfosalts. ## Differentiation from Similar Minerals This mineral is most often confused with sartorite, in which it forms inclusions, as well as with other minerals from the sartorite group, such as dufrénoysite or baumhauerite. The differences between them are subtle and mainly concern the proportions of metals (silver, lead, arsenic), which can only be determined by analytical methods. ## Crystal Forms Argentodufrénoysite occurs exclusively in the form of anhedral, irregular grains ranging in size from a few to about 100 micrometers. These grains are always intergrown with other minerals, most often with sartorite.

Geological environment

## Genesis Argentodufrénoysite forms under hydrothermal conditions in polymetallic deposits. Its formation is associated with crystallization from solutions rich in arsenic, sulfur, lead, and silver under specific pressure and temperature conditions. ## Mineral Associations This mineral occurs almost exclusively in paragenesis with sartorite, often forming microscopic inclusions within it. It also co-occurs with other lead and arsenic sulfosalts, such as dufrénoysite, baumhauerite, as well as with realgar, orpiment, and pyrite. ## Localities The only confirmed occurrence (type locality) of argentodufrénoysite in the world is the Lengenbach quarry in the Binn Valley (Binntal) in the canton of Valais, Switzerland. This is a classic locality for many rare sulfosalts.

Rarity

Extremely rare

For collectors

## Quality Criteria Argentodufrénoysite does not form collector specimens in the traditional sense. Its value is purely scientific and systematic. For specialized micromineral collections (so-called "micromounts"), samples with analytically confirmed presence of this mineral, originating from the type locality, may be valuable. ## Popular Localities The only source of material for research and systematic collections is the Lengenbach quarry in Switzerland.

Care and storage

## Cleaning Due to its microscopic nature and occurrence as inclusions, specimens are not subject to cleaning in the typical sense. Any attempts to mechanically or chemically separate the mineral from the rock matrix lead to its destruction. ## What to Avoid Avoid contact with acids and other aggressive chemicals that may react with sulfides. Specimens containing argentodufrénoysite should be protected from moisture to prevent oxidation of co-occurring minerals. ## Storage Storage in dry conditions, in sealed containers or mineralogical display cases, is sufficient to protect specimens. There are no special requirements regarding light exposure or temperature.

Sources

IMA Mineral List (CNMNC)