Kenoargentotetrahedrite-(Zn)

Chemical formula: [Ag₆]₄+(Cu₁+₄Zn₂+₂)Sb₃+₄S₂-₁₂&#₉₇₄₄;

A rare mineral from the tetrahedrite group, being the zinc-rich and silver-rich member of this complex sulfosalt family.

## Characteristics Kenoargentotetrahedrite-(Zn) is a rare mineral belonging to the tetrahedrite group, characterized by a complex chemical composition dominated by silver, copper, zinc, antimony, and sulfur. It typically forms small, granular aggregates or occurs as inclusions within other ore minerals. Well-formed crystals are extremely rare and exhibit the typical tetrahedrite group morphology, i.e., tetrahedra, often with modified faces. Its color is steel-gray to almost black, with a distinct metallic luster. ## Physical Properties This mineral is characterized by a metallic luster and is opaque. Its Mohs hardness ranges from 3.5 to 4, meaning it is relatively soft. It has a rather high density, approximately 5.1 g/cm³, which is typical for sulfosalts containing heavy metals like silver and antimony. ## Colors and Varieties Kenoargentotetrahedrite-(Zn) occurs in a uniform, steel-gray or black color. Due to its rarity and specific chemical composition, no color varieties or commercial names are distinguished for it. ## History and Name The mineral's name is complex and reflects its characteristics. The prefix "keno-" (from Greek "empty") indicates a vacancy in one of the structural positions. "Argento" refers to silver (Latin *argentum*) as the dominant element. "Tetrahedrite" indicates its belonging to the tetrahedrite group and its typical crystal form. The "-(Zn)" suffix specifies that zinc is the dominant divalent metal in this particular variety. The mineral was formally recognized by the International Mineralogical Association (IMA) in 2018. ## Uses Due to its extreme rarity, kenoargentotetrahedrite-(Zn) has no industrial applications. It is of purely scientific significance, serving as an object of mineralogical and crystal-chemical research, and is highly valued by specialized collectors of rare minerals.

Properties

Mohs hardness: 3.5-4
Luster: Metallic
Streak: Black
Density: 5.1
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identifying kenoargentotetrahedrite-(Zn) is extremely difficult without advanced analytical methods. Preliminary identification in the field or in a collection relies on its steel-gray to black color, metallic luster, relatively low hardness, and co-occurrence with other silver sulfosalts and ore minerals. Definitive identification requires chemical composition analysis (EDS/WDS) and often X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be easily confused with other members of the tetrahedrite group, such as tetrahedrite-(Zn), tetrahedrite-(Fe), argentotetrahedrite-(Fe), or freibergite. Visually, they are practically indistinguishable. They differ in the proportions of silver, copper, iron, zinc, and other elements, which can only be determined by chemical analysis. From other similar sulfosalts (e.g., bournonite, stephanite), it is distinguished by its crystal form (if visible) and specific mineral associations. ## Crystal Forms Crystals, though extremely rare, adopt a tetrahedral form, which is characteristic of the entire group. It usually occurs as anhedral (irregular) grains or as microscopic inclusions in other minerals.

Geological environment

## Genesis Kenoargentotetrahedrite-(Zn) forms through hydrothermal processes, crystallizing in medium- to low-temperature ore veins. It is associated with polymetallic deposits rich in silver, antimony, and base metals. ## Mineral Associations This mineral co-occurs with other sulfosalts and sulfides. In its type locality (Uchucchacua mine), it was found in association with pyrargyrite, polybasite, acanthite, galena, sphalerite, pyrite, quartz, and alabandite. Its occurrence with other silver-rich minerals is characteristic. ## Localities The most important and also the type locality for this mineral is the Uchucchacua mine in Oyon Province, Lima Region, Peru. This is a world-renowned deposit known for the occurrence of many rare silver sulfosalts. Outside of Peru, its presence has been reported in the Kutná Hora mine in the Czech Republic.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a kenoargentotetrahedrite-(Zn) specimen is almost exclusively determined by the possibility of its identification and documentation. Since this mineral usually occurs as microscopic grains, any specimen in which it is visible to the naked eye or under slight magnification is considered exceptional. The most highly prized samples are those from a well-documented type locality (Uchucchacua), where the mineral forms rich aggregates or, extremely rarely, visible crystals. Association with other well-formed, rare minerals is also important. ## Popular Localities The only significant locality from a collector's perspective is the Uchucchacua mine in Peru. Specimens originating from there are the most sought after by specialized collectors.

Care and storage

## Cleaning Specimens of this mineral should be cleaned very carefully, preferably using compressed air to remove dust. If wet cleaning is necessary, use only a small amount of distilled water or isopropyl alcohol on a soft brush, then immediately and thoroughly dry the specimen. Avoid ultrasonic cleaners. ## What to Avoid Contact with acids and other aggressive chemicals, which can quickly destroy the mineral, must be absolutely avoided. As a sulfide, it is susceptible to oxidation, so it should be protected from prolonged exposure to moisture and air, which can lead to its slow decomposition and the formation of secondary minerals. It should not be heated or exposed to sudden temperature changes. ## Storage The best way to store specimens is in a dry, airtight container (e.g., a "perky box") away from direct sunlight and heat sources. Consider using desiccants in the display cabinet or container where the mineral is stored.

Sources

IMA Mineral List (CNMNC)