Zvĕstovite-(Fe)

Chemical formula: Ag₁+₆(Ag₁+₄Fe₂+₂)As₃+₄S₂-₁₃

Zvĕstovite-(Fe) is a very rare, silvery-black sulfide of silver, iron, and arsenic, forming microscopic, metallic-lustered crystals.

## Characteristics Zvĕstovite-(Fe) is a mineral from the sulfosalt group, belonging to the tetrahedrite mineral series. It forms very small, isometric crystals, most often in the form of tetrahedra, which rarely exceed 0.2 mm in size. It occurs as single, well-formed crystals or small aggregates thereof. Its color is black, and on fresh surfaces, it exhibits a strong, metallic luster. ## Physical Properties This mineral is opaque and brittle. Its Mohs hardness ranges from 3.5 to 4, and its density, calculated based on the chemical formula and unit cell parameters, is 5.51 g/cm³. It exhibits a black streak with a brownish tint. ## History and Name Zvĕstovite-(Fe) was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2019 (IMA2019-017). Its name comes from its type locality – the historic Zvěstov deposit in the Czech Republic. The "(Fe)" suffix in the name indicates that iron (Latin: *ferrum*) is the dominant divalent metal in its structure, distinguishing it from hypothetical or future-discovered counterparts with other elements, such as zinc (Zn) or copper (Cu).

Properties

Mohs hardness: 3.5-4
Luster: Metallic
Streak: Black with a brownish tint
Density: 5.51
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of Zvĕstovite-(Fe) is impossible without advanced analytical techniques. It requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm the composition with dominant iron, and X-ray diffraction (XRD) to determine the crystal structure. Visually, within its paragenesis, it can be suspected based on its black color, metallic luster, and tetrahedral crystal form. ## Distinguishing from Similar Minerals This mineral is visually indistinguishable from other members of the tetrahedrite group, such as tetrahedrite, freibergite, or argentotetrahedrite. Definitive differentiation is only possible based on precise chemical composition analysis. ## Crystal Forms It crystallizes in the isometric system, primarily forming tetrahedral crystals, often with modifications of other faces. The crystals are very small, not exceeding several hundred micrometers in size.

Geological environment

## Genesis Zvĕstovite-(Fe) forms as a result of hydrothermal processes in polymetallic ore veins rich in silver and arsenic. In its type locality (Zvěstov), it occurs in calcite-quartz veins cutting gneisses. ## Mineral Associations This mineral co-occurs with other sulfides and sulfosalts. In its paragenesis, acanthite, native arsenic, stephanite, pyrargyrite, proustite, galena, sphalerite, chalcopyrite, and other minerals from the tetrahedrite group have been identified, among others. ## Localities The only confirmed and described locality for Zvĕstovite-(Fe) in the world is its place of discovery – the historic mining district of Zvěstov, located east of the town of Vlašim in the Central Bohemian Region of the Czech Republic.

Rarity

Extremely rare

For collectors

## Quality Criteria As a mineral of primarily scientific and systematic importance, specimens where Zvĕstovite-(Fe) forms well-developed, sharp, and lustrous microcrystals are most highly valued. The ability to unambiguously identify the mineral on the specimen and the richness of its association with other rare silver sulfosalts are key. Every analytically confirmed specimen is extremely valuable for advanced systematic collections. ## Popular Localities The only source of specimens is the type locality in the Czech Republic (Zvěstov). Material from this location is extremely difficult to acquire.

Care and storage

## Cleaning Due to its extreme rarity and microscopic crystal size, mechanical cleaning is not recommended and should only be performed by specialists under laboratory conditions. Specimens should be handled with utmost caution. ## What to Avoid Contact with chemicals, acids, and bases, which can damage the mineral, should be avoided. As a sulfide, it is susceptible to oxidation, so it should be protected from moisture and prolonged exposure to air, which can lead to its slow decomposition and loss of luster. ## Storage Zvĕstovite-(Fe) specimens should be stored under stable conditions, in specialized, airtight "micromount" containers or system boxes, away from dust, moisture, and chemical contaminants. Protection against oxidation is crucial for preserving its scientific and aesthetic value.