Eleomelanite

Chemical formula: (K₂Pb₂+)Cu₂+₄O₂(S₆+O₄)₄

Eleomelanite is a rare potassium, lead, and copper sulfate, forming black, tabular crystals with a metallic luster.

## Characteristics Eleomelanite is a mineral from the sulfate group, distinguished by its complex chemical composition containing potassium, lead, and copper. It forms very small, black, tabular or lamellar crystals, which usually do not exceed 0.2 mm. They are observed as single crystals or small aggregates. The mineral is opaque and characterized by a metallic luster. ## Physical Properties Eleomelanite crystals are brittle. Due to the small size of the crystals, precise determination of hardness and density has not been possible. The density was calculated based on the chemical formula and unit cell parameters and is 4.49 g/cm³. ## Colors and Varieties Eleomelanite occurs exclusively in black. No color varieties or commercial forms are known. ## History and Name The mineral's name comes from the Greek words ελαίον (elaion - oil) and μέλας (melas - black), referring to its appearance resembling black, oily drops. It was discovered in volcanic exhalations (fumaroles) at Tolbachik volcano in Kamchatka, Russia. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2015 (IMA2015-058). It was described by a team of mineralogists led by Igor V. Pekov. ## Applications Eleomelanite has no industrial applications. Its significance is purely scientific and collectible, as a rare and recently discovered mineral.

Properties

Luster: Metallic
Streak: Black
Density: 4.49
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Eleomelanite is identified by its unique appearance – black, shiny, tabular crystals occurring in a specific environment. Identification requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS), due to the microscopic size of the crystals and similarity to other black volcanic minerals. ## Distinguishing from Similar Minerals It can be confused with other black minerals from the fumaroles of Tolbachik volcano, such as tenorite (CuO) or other complex sulfates. Visual distinction is practically impossible and requires specialized research equipment. The crystal shape (thin tablets) can be a helpful clue, but it is not an unambiguously diagnostic feature. ## Crystal Forms Eleomelanite crystallizes in the form of very thin, tabular or lamellar crystals, often with a hexagonal outline. It also forms irregular aggregates and clusters of these crystals.

Geological environment

## Genesis Eleomelanite is a mineral of volcanic origin. It forms through sublimation from volcanic gases in fumaroles, which are high-temperature exhalations (above 600°C). It crystallizes directly from the gas phase on the surface of volcanic rocks, such as basalt. ## Mineral Associations This mineral co-occurs with other sulfates and oxides formed under similar conditions. At the type locality (Tolbachik volcano), it was found in association with minerals such as anglesite, chalcanthite, dolangfanite, euchlorine, langbeinite, tenorite, and wulffite. ## Localities The only confirmed locality for eleomelanite worldwide is its type locality – the "Arsenatnaya" fumarole on the second cinder cone of the Northern Breakthrough of the Great Fissure Eruption of Tolbachik volcano in Kamchatka, Russia.

Rarity

Very rare

For collectors

## Quality Criteria As a "micromount" type mineral, the collectible value of eleomelanite depends on the quality and size of the crystals, although these rarely exceed fractions of a millimeter. The most prized specimens are those with well-formed, sharp, shiny crystals, clearly visible against the matrix rock. Rich aggregates of crystals are more desirable than single, isolated individuals. ## Popular Localities The only source of eleomelanite specimens is Tolbachik volcano in Kamchatka. Material from this locality is extremely rare and sought after by specialized collectors of volcanic minerals and rare species.

Care and storage

## Cleaning Due to the extreme brittleness and small size of the crystals, mechanical cleaning is not recommended. Specimens should be protected from dust by storing them in sealed containers. If cleaning is absolutely necessary, compressed air can be used from a safe distance. ## What to Avoid Avoid contact with water and all chemicals, as the mineral may be soluble or reactive. The crystals are very brittle and sensitive to any shocks and touch. Avoid ultrasound and temperature changes. ## Storage Eleomelanite specimens should be stored under stable conditions, in specialized "micromount" boxes or sealed display cases, away from vibrations, moisture, and contaminants. It is best to store them in the original container in which they were acquired.

Sources

IMA Mineral List (CNMNC)