Zvĕstovite-(Zn)

Chemical formula: Ag₁+₆(Ag₁+₄Zn₂+₂)As₃+₄S₂-₁₃

Zvĕstovite-(Zn) is a very rare silver, zinc, and arsenic sulfide from the tetrahedrite group, discovered in the Czech Republic.

## Characteristics Zvĕstovite-(Zn) is a mineral from the tetrahedrite group, defined as a zinc- and arsenic-rich member of this group. It occurs as metallic-looking, black grains up to several hundred micrometers in size, often intergrown with other sulfides. Its grains are typically anhedral (do not exhibit their own crystallographic forms) and can only be observed under a microscope in polished sections. ## Physical Properties This mineral is characterized by a metallic luster and a black streak. It is opaque. Its Mohs hardness ranges from 3.5 to 4, and its calculated density is approximately 5.45 g/cm³. It does not exhibit cleavage, and its fracture is uneven. ## History and Name Zvĕstovite-(Zn) was officially recognized by the International Mineralogical Association (IMA) in 2020 (IMA2020-035). Its name comes from its type locality – the historic Zvěstov deposit near Vlašim in the Czech Republic. The "-(Zn)" suffix in the name indicates the dominance of zinc at a specific site in the crystal structure, according to the tetrahedrite group nomenclature.

Properties

Mohs hardness: 3.5-4
Luster: Metallic
Streak: Black
Density: 5.45
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of Zvĕstovite-(Zn) is impossible without advanced laboratory techniques. It requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to determine the composition and proportions of silver, zinc, and arsenic. In polished sections under a reflected light microscope, it has a grayish-white color with a greenish tint and is isotropic. ## Distinguishing from Similar Minerals It is visually indistinguishable from other black, metallic minerals of the tetrahedrite group, such as tetrahedrite, freibergite, argentotetrahedrite, or tennantite. Differentiation relies solely on precise chemical composition analysis. ## Crystal Forms Observed exclusively in the form of anhedral (irregular) grains, forming aggregates or inclusions in other minerals.

Geological environment

## Genesis Zvĕstovite-(Zn) forms in hydrothermal veins containing polymetallic ore mineralization. In its type locality (Zvěstov), it occurs in quartz-siderite veins cutting gneisses. ## Mineral Associations This mineral co-occurs with other sulfides and sulfosalts. In the Czech Republic, it has been found in association with stephanite, polybasite, pyrargyrite, chalcopyrite, sphalerite, galena, pyrrhotite, arsenopyrite, acanthite, and other minerals of the tetrahedrite group. ## Localities The only confirmed and described locality in the world is the historic mining area of Zvěstov, east of the town of the same name, in the Central Bohemian Region of the Czech Republic.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the collector's value of Zvĕstovite-(Zn) is not based on aesthetics but on its extreme rarity and scientific significance. The most valuable specimens are those where the presence of the mineral has been analytically confirmed, and its grains are as "rich" and well-visible as possible in association with other rare minerals. A specimen is de facto a fragment of rock containing microscopic grains of the mineral.

Care and storage

## Cleaning Specimens of this mineral are generally not cleaned due to their microscopic size and embedding in the host rock. Any attempts at mechanical or chemical cleaning may damage the delicate grains. ## What to Avoid Avoid contact with chemicals, acids, and cleaning agents. As a sulfide, it may be susceptible to oxidation in humid environments. Avoid ultrasonic cleaners and sudden temperature changes. ## Storage Store in stable, dry conditions, preferably in a closed display box to protect against dust and moisture. Microscopic specimens should be stored in specialized "micromount" boxes.

Sources

IMA Mineral List (CNMNC)