Argentotetrahedrite-(Hg)

Chemical formula: Ag₁+₆(Cu₁+₄Hg₂+₂)Sb₃+₄S₂-₁₃

A rare mineral from the tetrahedrite group, a mercury-rich variety of argentotetrahedrite, with a metallic luster and steel-gray color.

## Characteristics Argentotetrahedrite-(Hg) is a rare mineral from the tetrahedrite group, belonging to the sulfosalt class. Chemically, it is a complex sulfide of silver, copper, mercury, and antimony. It occurs as embedded, poorly formed tetrahedral crystals, as well as granular and massive aggregates. Its surface has a characteristic, strong metallic luster, and its color ranges from steel-gray to almost black. ## Physical Properties This mineral has a hardness of 3-4 on the Mohs scale, making it relatively soft. It is brittle, and its fracture is uneven to conchoidal. The density is quite high, approximately 5.3 g/cm³. It is an opaque mineral with a metallic luster. The streak on a streak plate is black. ## Colors and Varieties Argentotetrahedrite-(Hg) has a uniform color, from steel-gray to black. As a specific member of an isomorphic series with mercury in its composition, it is itself a specific variety of argentotetrahedrite. No additional color or commercial varieties are distinguished for it. ## History and Name The mineral's name directly refers to its chemical composition. The prefix "Argento" indicates the dominance of silver (Latin: *argentum*), "tetrahedrite" refers to its membership in the tetrahedrite group and typical crystal form (tetrahedron), and the suffix "-(Hg)" signifies that mercury (symbol Hg) is the dominant divalent element in its structure. It was formally described and approved as a new mineral species by the International Mineralogical Association (IMA) in 2019. ## Uses Due to its extreme rarity, argentotetrahedrite-(Hg) has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of systematic and rare minerals.

Properties

Mohs hardness: 3-4
Luster: Metallic
Streak: Black
Density: 5.3
Cleavage: None
Fracture: Uneven to subconchoidal
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identifying argentotetrahedrite-(Hg) under amateur conditions is practically impossible and requires advanced analytical methods, such as chemical composition analysis (EDS/WDS). Preliminarily, it can be recognized by its steel-gray color, metallic luster, black streak, and co-occurrence with other silver and mercury sulfosalts. It is relatively soft and brittle. ## Distinguishing from Similar Minerals This mineral is visually indistinguishable from other members of the tetrahedrite group, such as tetrahedrite, freibergite (argentotetrahedrite), or schwatzite-(Hg). It can also be confused with other sulfosalts of similar appearance, e.g., enargite, stephanite, or polybasite. Definitive differentiation is only possible based on chemical analysis. ## Crystal Forms It crystallizes in the isometric system, most often forming crystals with a tetrahedral habit, often with modifications of other faces. Crystals are usually small, embedded in the host rock or other minerals. It also occurs in the form of granular aggregates and masses filling small spaces.

Geological environment

## Genesis Argentotetrahedrite-(Hg) is a hydrothermal mineral. It forms in ore veins that develop under low to medium temperature conditions. It is a product of crystallization from solutions rich in silver, copper, mercury, antimony, and sulfur. ## Mineral Associations It most often co-occurs with other ore minerals. In its type locality (Kremnica mine in Slovakia), it was found in association with quartz, dolomite, calcite, pyrite, chalcopyrite, sphalerite, galena, stibnite, as well as other, rarer silver and mercury sulfosalts. ## Localities This is an extremely rare mineral. Its type locality is the Schrämen vein in the Kremnica mine, Slovakia. In addition, single finds have been reported from the Lengenbach quarry in the Binn Valley, Switzerland, and the Uchucchacua mine in Oyon Province, Peru. These are the only confirmed occurrences worldwide.

Rarity

Extremely rare

For collectors

## Quality Criteria The most important criterion for collectors' value is the confirmation of the mineral's identity through chemical analysis. Specimens with well-formed, sharp tetrahedral crystals, even if small, are highly prized. The aesthetic composition with associated minerals, such as quartz or dolomite, and the absence of mechanical damage, are also important. Luster and surface purity also increase the specimen's value. ## Popular Localities Specimens from the type locality – the Kremnica mine in Slovakia – are by far the most valued and sought after. Material from this location serves as the standard for the species and is extremely difficult to obtain.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to the presence of mercury and antimony, inhalation of dust should be avoided. After contact with the mineral, it is recommended to wash hands. The use of water, especially acids, is prohibited. ## What to Avoid Avoid contact with chemicals, particularly acids, which can damage it. The mineral is susceptible to oxidation, so it should be protected from moisture and prolonged exposure to air, which can cause its surface to tarnish. It should not be heated. ## Storage It is recommended to store specimens in sealed, dry containers (e.g., membrane boxes or mineral display cases) at a stable room temperature. Limiting access to air and moisture will help preserve the mineral's natural luster.

Sources

IMA Mineral List (CNMNC)