Eliopoulosite

Chemical formula: V<sub>₇</sub>S<sub>₈</sub>

Eliopoulosite is a very rare vanadium sulfide, forming fine, metallic grains in ultramafic rocks.

## Characteristics Eliopoulosite is a vanadium sulfide with a metallic luster. It occurs as very small, anhedral (irregularly shaped) grains, usually not exceeding 100 micrometers in size. These grains are most often intergrown with chromite or minerals from the serpentine group. Due to its size and mode of occurrence, individual crystals are not visible to the naked eye, and the mineral can only be identified using advanced analytical techniques, such as electron microscopy. ## Physical Properties The Mohs hardness of eliopoulosite is approximately 4. It is an opaque mineral with a metallic luster and a black streak. Its density, calculated based on the chemical formula and unit cell parameters, is 4.59 g/cm³. ## Colors and Varieties This mineral has a brownish or reddish-brown color with a metallic sheen. No varieties have been distinguished. ## History and Name Eliopoulosite was recognized as a new mineral by the International Mineralogical Association (IMA) in 2006. Its name honors Elias P. Eliopoulos (1938–1997), a Greek geologist from the Institute of Geology and Mineral Exploration in Athens, for his contributions to the study of Greek ore deposits. The type locality (place of discovery) is the Korydallos chromite mine in the Pindos Mountains, Greece. ## Uses Due to its extreme rarity and occurrence as microscopic grains, eliopoulosite has no commercial or industrial applications. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 4
Luster: Metallic
Streak: Black
Density: 4.59
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Identification of eliopoulosite is impossible without specialized equipment. Recognition is based on chemical analysis using an electron microprobe (EDS/WDS) to confirm the composition (vanadium to sulfur ratio). Visual characteristics, such as brownish color, metallic luster, and co-occurrence with chromite in ultramafic rocks, can only suggest its possible presence. ## Distinguishing from Similar Minerals Eliopoulosite can be confused with other metallic sulfides, such as pyrrhotite, pentlandite, or other vanadium sulfides (e.g., patronite). Definitive differentiation requires precise chemical composition analysis, as the physical properties of these minerals, especially as fine grains, are very similar. ## Crystal Forms This mineral forms exclusively anhedral, irregular grains and aggregates. Its occurrence in the form of well-developed crystals has not been observed.

Geological environment

## Genesis Eliopoulosite forms in a specific geological environment – in suprasubduction zone ophiolites. It is a mineral of magmatic origin, crystallizing in chromite-rich lenses within ultramafic rocks (dunites, harzburgites) that have undergone serpentinization processes. ## Mineral Associations This mineral occurs in close association with chromite. It is also accompanied by other, often rare sulfides, such as patronite, minerals from the linnaeite group (e.g., siegenite), as well as laurite, millerite, and chalcopyrite. ## Localities Eliopoulosite is an extremely rare mineral. Besides the type locality in the Korydallos mine in Greece, its presence has also been reported in the Kempirsai massif in Kazakhstan and in ophiolites in the Polar Urals in Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to the microscopic nature of the mineral, collector specimens are practically fragments of the host rock (chromitite) containing analytically confirmed eliopoulosite. Samples from the type locality are most highly valued, especially those that have been analyzed and have scientific documentation. The value of a specimen increases with the abundance of eliopoulosite and the presence of other rare associated minerals. Polished sections used in scientific research also have high value for specialized collectors. ## Popular Localities The only source of specimens available on the collector's market is its type locality – the Korydallos mine in the Pindos Mountains, Greece.

Care and storage

## Cleaning Specimens containing eliopoulosite are generally not cleaned due to the microscopic size of the grains and their embedding in the rock matrix. Any attempt at chemical or mechanical cleaning could damage or remove the mineral. If necessary, dust can be removed with a soft brush or compressed air from a safe distance. ## What to Avoid Avoid contact with all chemicals, especially acids, which can react with sulfides. The mineral should be protected from moisture and sudden temperature changes to prevent potential oxidation. ## Storage Eliopoulosite specimens are best stored in stable conditions, in a closed, dry container (e.g., a "perky box"), to protect them from dust and humidity changes. Polished sections (thin sections) used for microscopic analysis should be stored in special containers to prevent surface scratching.

Sources

IMA Mineral List (CNMNC)