Argentotetrahedrite-(Cd)

Chemical formula: Ag₁+₆(Cu₁+₄Cd₂+₂)Sb₃+₄S₂-₁₃

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

## Characteristics Argentotetrahedrite-(Cd) is a rare sulfosalt mineral from the tetrahedrite group, belonging to the argentotetrahedrite series. Chemically, it is a complex sulfide of silver, copper, cadmium, and antimony. It occurs as inclusions in other minerals, rarely forming small, poorly developed crystals with a tetrahedral outline. It is usually found in granular aggregates or as irregular masses. Its color is steel-gray to black, and on a fresh surface, it exhibits a strong, metallic luster. ## Physical Properties This mineral is characterized by a hardness of 3.5-4 on the Mohs scale. It has a metallic luster and is opaque. Its density, calculated based on the chemical formula and unit cell parameters, is approximately 5.33 g/cm³. It shows no cleavage, and its fracture is uneven to conchoidal. ## Colors and Varieties Argentotetrahedrite-(Cd) occurs in a uniform, steel-gray or black color. As a mineral defined by the dominance of cadmium in a specific site of the crystal structure, it is itself a specific variety within the tetrahedrite group. No further color or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition and structure. The prefix "Argento" indicates the dominance of silver, "tetrahedrite" refers to its belonging to the tetrahedrite group and its typical tetrahedral crystal form, and the suffix "-(Cd)" signifies that cadmium is the dominant divalent element in its structure. The mineral was approved by the International Mineralogical Association (IMA) in 2018. It was discovered in the Uchucchacua mine in Peru. ## Uses Due to its extreme rarity, argentotetrahedrite-(Cd) has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals.

Properties

Mohs hardness: 3.5-4
Luster: Metallic
Streak: Black
Density: 5.33
Cleavage: None
Fracture: Uneven to conchoidal
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of argentotetrahedrite-(Cd) is extremely difficult and impossible without advanced analytical methods. Preliminary identification based on visual characteristics, such as steel-gray color, metallic luster, and co-occurrence with other silver sulfosalts, can only suggest the presence of a mineral from the tetrahedrite group. Definitive confirmation requires chemical analysis (e.g., using an electron microprobe) to ascertain the dominance of silver, cadmium, and antimony in the appropriate structural positions. ## Distinguishing from Similar Minerals This mineral is visually indistinguishable from other members of the tetrahedrite group, such as tetrahedrite, tenantite, freibergite, or argentotetrahedrite-(Zn). All these minerals have similar color, luster, and mode of occurrence. Certain differentiation is only possible based on detailed chemical analysis. ## Crystal Forms Argentotetrahedrite-(Cd) crystallizes in the isometric system. Its crystals, if at all developed, take the form of tetrahedra, often with modifications of other faces. However, it usually occurs as irregular grains or massive aggregates intergrown with other minerals.

Geological environment

## Genesis Argentotetrahedrite-(Cd) is a hydrothermal mineral. It forms in ore veins that developed at medium and low temperatures. In its type locality (Uchucchacua mine), it is associated with Mesozoic volcano-sedimentary rocks. ## Mineral Associations This mineral co-occurs with other sulfides and sulfosalts. At the discovery site, its association with pyrite, sphalerite, galena, chalcopyrite, quartz, rhodochrosite, alabandite, gratonite, proustite, manganese pyroxenes, and other members of the tetrahedrite group was noted. ## Localities The only confirmed and described locality for argentotetrahedrite-(Cd) in the world is the Uchucchacua mine, in Oyon Province, Lima Region, Peru. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The collector quality of argentotetrahedrite-(Cd) specimens is difficult to assess in a traditional way, as this mineral primarily occurs as microscopic grains or inclusions. The most valuable specimens are those in which the mineral has been unequivocally identified by chemical analysis, and its presence is documented. The value of a specimen increases if argentotetrahedrite-(Cd) forms rare, macroscopic aggregates or poorly developed microcrystals. Authenticity confirmed by a reputable laboratory is crucial. ## Popular Localities The only source of specimens of this mineral is its type locality – the Uchucchacua mine in Peru. All specimens available on the collector's market (though extremely rare) originate from this single location.

Care and storage

## Cleaning Specimens of this mineral should generally not be cleaned wet. Any contaminants, such as dust, are best removed very carefully using a soft brush or compressed air from a safe distance. ## What to Avoid Avoid contact with water, acids, detergents, and other chemicals that can cause chemical reactions on the mineral's surface and lead to permanent damage or loss of luster. The mineral is relatively soft and brittle, so it should be protected from impacts and scratches. ## Storage Argentotetrahedrite-(Cd) specimens should be stored under stable conditions, in a dry environment, away from direct sunlight and heat sources. It is best to place them in a sealed display box away from other minerals that could scratch them.

Sources

IMA Mineral List (CNMNC)