Vihorlatite

Chemical formula: Bi₂₄Se₁₇Te₄

Vihorlatite is a rare bismuth selenide with tellurium, forming acicular crystals with a metallic luster, discovered in Slovakia.

## Characteristics Vihorlatite is a mineral from the sulfide group, more specifically a complex bismuth selenide with an admixture of tellurium. It forms very fine, acicular or hair-like crystals, rarely exceeding 1 mm in length. They usually occur as tangled aggregates or radial clusters embedded in quartz. The mineral is characterized by a metallic luster and a steel-gray to tin-white color. ## Physical Properties Vihorlatite crystals are flexible and pliable. Due to their small size and form of occurrence, precise determination of hardness and density is difficult. The density calculated based on the chemical formula and unit cell parameters is 8.35 g/cm³. ## History and Name The mineral's name comes from the Vihorlat volcanic mountain range in eastern Slovakia, where it was discovered. Vihorlatite was approved as a new mineral by the International Mineralogical Association (IMA) in 2017 (IMA2017-026). Its discovery is the result of mineralogical research in the Poruba pod Vihorlatom area. ## Uses Vihorlatite has no industrial applications. It is solely an object of scientific and collecting interest due to its rarity and specific chemical composition.

Properties

Luster: Metallic
Streak: Black
Density: 8.35
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Amateur identification of vihorlatite is practically impossible. This mineral is distinguished by its form of occurrence – as very fine, flexible, acicular crystals with a metallic luster, most often embedded in quartz. Certain identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS) to confirm the chemical composition (presence of Bi, Se, and Te). ## Distinguishing from Similar Minerals Vihorlatite can be confused with other acicular sulfosalts or bismuth selenides, such as bismuthinite, aikinite, or lillianite. Differentiation is based on chemical analysis, which shows the dominance of selenium over sulfur and the presence of tellurium. Visually, it is almost indistinguishable from similar minerals without specialized equipment. ## Crystal Forms Vihorlatite exclusively forms acicular or hair-like crystals, elongated along the c-axis. These crystals occur individually or form tangled, woolly aggregates and radial clusters.

Geological environment

## Genesis Vihorlatite is a mineral of hydrothermal origin. It forms in low-temperature, epithermal quartz veins that cut through andesites and their tuffs. Its crystallization is associated with Neogene volcanic activity. ## Mineral Associations This mineral occurs in paragenesis with quartz (often in its amethyst variety), pyrite, chalcopyrite, galena, sphalerite, hematite, as well as other, rarer bismuth selenides and tellurides, such as lillianite, neyite, or ikunolite. ## Localities The only confirmed locality of vihorlatite in the world is its type locality – an andesite quarry in the village of Poruba pod Vihorlatom, in the Košice Region, Slovakia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a vihorlatite specimen is primarily assessed based on the richness and visibility of its crystals. The most valued samples are those where the acicular or radial aggregates are well-formed, abundant, and clearly contrast with the quartz matrix. Due to the microscopic nature of the mineral, specimens are usually small (so-called "micromounts"). ## Popular Localities The only source of vihorlatite specimens is the quarry in Poruba pod Vihorlatom, Slovakia. Material from this locality is extremely rare on the collector's market.

Care and storage

## Cleaning Specimens of vihorlatite should be cleaned very carefully, preferably using compressed air to remove dust. Due to the delicate nature of the acicular crystals, any mechanical contact, including brushing, should be avoided. Washing in water, especially with detergents, is not recommended. ## What to Avoid Avoid contact with chemicals that could react with selenides and tellurides. The mineral should be protected from extreme temperatures and humidity. Prolonged exposure to strong light is not advisable, although there is no detailed data on its photosensitivity. ## Storage It is recommended to store specimens in closed, stable containers (e.g., "micromount" boxes) to protect delicate crystals from mechanical damage and dust. Display should be in controlled conditions, away from vibrations and direct sunlight.

Sources

IMA Mineral List (CNMNC)