Annivite-(Zn)

Chemical formula: Cu₁+₆(Cu₁+₄Zn₂+₂)Bi₃+₄S₂-₁₃

Annivite-(Zn) is a rare copper, zinc, and bismuth sulfide, forming small, metallic anhedral inclusions within other minerals.

## Characteristics Annivite-(Zn) is a very rare mineral from the tetrahedrite group, formally defined as its zinc and bismuth analog. It occurs as very fine, anhedral (irregularly shaped) grains, usually as inclusions in other sulfides, such as chalcopyrite. Due to the microscopic size of the crystals, its visual features are difficult to observe without specialized equipment. Under a polarizing microscope in reflected light, it appears gray with an olive tint. ## Physical Properties Due to its microscopic mode of occurrence, most physical properties, such as hardness, density, or luster, have not been precisely measured for pure material. Hardness is estimated based on analogy with other minerals of the tetrahedrite group to be approximately 3-4 on the Mohs scale. The density calculated from the chemical formula and unit cell parameters is 5.25 g/cm³. The mineral is opaque and exhibits a metallic luster. ## History and Name The name "annivite" comes from the discovery locality of the original annivite (a bismuth variety of tetrahedrite) in the Val d'Anniviers in Switzerland. The suffix "-(Zn)" was added in accordance with the nomenclature rules of the International Mineralogical Association (IMA) to indicate that zinc is the dominant divalent metal in this particular variety. The mineral was formally described and approved as a new species in 2021.

Properties

Mohs hardness: 3-4
Luster: Metallic
Streak: Black
Density: 5.25
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of annivite-(Zn) is impossible without advanced analytical techniques. It requires chemical analysis using an electron microprobe (EDS/WDS) to confirm the presence and proportions of copper, zinc, bismuth, and sulfur. Observations in reflected light under a microscope can provide preliminary indications but are not sufficient for unambiguous identification. ## Distinguishing from Similar Minerals Annivite-(Zn) is visually indistinguishable from other minerals of the tetrahedrite group, such as tetrahedrite, tennantite, freibergite, or annivite itself (without zinc). Differentiation relies solely on precise chemical analysis. ## Crystal Forms This mineral has only been observed in the form of anhedral, i.e., irregular, grains with sizes not exceeding 100 micrometers. Well-formed crystals have not been observed.

Geological environment

## Genesis Annivite-(Zn) forms as a result of hydrothermal processes. At its type locality (Biely Vrch mine in Slovakia), it crystallized in the late stage of mineralization from bismuth-rich solutions, at a temperature of approximately 200-250°C. It forms in polymetallic veins. ## Mineral Associations This mineral occurs in close association with chalcopyrite (often as inclusions within it), pyrite, sphalerite, galena, quartz, and other minerals of the tetrahedrite group. ## Localities The only confirmed and described locality for annivite-(Zn) is the Biely Vrch gold deposit in the Javorie mountain range in Slovakia. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria Annivite-(Zn) is a mineral of purely scientific and systematic importance, rather than a collector's item in the traditional sense. It does not form macroscopic specimens. Its "value" lies in the presence confirmed by analyses within the host rock, which makes such a specimen a valuable acquisition for specialized systematic and regional collections (so-called "micromounts").

Care and storage

## Cleaning Due to its occurrence as microscopic inclusions within the host rock, isolated cleaning of annivite-(Zn) itself is impossible and impractical. Specimens containing this mineral should be treated according to the requirements of the dominant mineral (e.g., chalcopyrite). ## What to Avoid Avoid contact with strong acids and chemical reagents, which can react with sulfides, leading to their damage or discoloration. Ultrasonic cleaners should also be avoided, as they can damage the delicate structure of the rock. ## Storage Specimens should be stored under stable conditions, away from moisture and chemical contaminants, to prevent oxidation of sulfides. It is best to keep them in closed display cases or collector boxes.

Sources

IMA Mineral List (CNMNC)