Murunskite

Chemical formula: K₂(Cu₁+,Cu₂+,Fe₂+)₄S₂-₄

Murunskite is a rare, opaque sulfide of potassium, copper, and iron, forming characteristic flakes and aggregates with a metallic luster.

## Characteristics Murunskite is a very rare mineral from the sulfide group. It occurs as small, thin, irregular flakes or scales, which can form rosette-like or scaly aggregates. Individual flakes rarely exceed 1 mm. It is an opaque mineral with a metallic luster and a characteristic brownish-violet color, which on fresh surfaces can transition into shades of brown. ## Physical Properties Murunskite is a soft mineral, with a Mohs hardness of 2. It exhibits perfect cleavage in one direction, which accounts for its flaky form. It has a metallic luster and a black streak. Its density is relatively high, approximately 4.23 g/cm³. ## Colors and Varieties This mineral is homogeneous in color and does not form varieties. Its typical color is brownish-violet to brown on fresh fracture surfaces. When exposed to air, its surface may tarnish and darken. ## History and Name Murunskite was discovered and described in 1984. Its name comes from its discovery locality – the Murun Massif in Russia (Irkutsk Oblast and Yakutia), which is its type locality. It was approved as a new mineral species by the International Mineralogical Association (IMA). ## Uses Due to its extreme rarity and small crystal sizes, murunskite has no industrial applications. It is solely an object of scientific interest and is valued by specialized collectors of rare minerals.

Properties

Mohs hardness: 2
Luster: Metallic
Streak: Black
Density: 4.23
Cleavage: Perfect on {001}
Fracture: Micaceous
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Murunskite can be identified by its characteristic brownish-violet color, metallic luster, flaky form, and perfect cleavage in one direction. Its occurrence is limited to a very specific geological environment. ## Distinguishing from Similar Minerals It can be confused with other flaky sulfides with a metallic appearance, such as covellite or molybdenite. However, it is distinguished by its specific brownish-violet color (covellite is indigo-blue, and molybdenite is lead-gray) and mineral association. Final confirmation requires advanced analytical methods (e.g., XRD, EDS). ## Crystal Forms It forms thin, flexible flakes and scales with irregular outlines. These crystals often occur as rosette-like, fan-shaped, or scaly aggregates and clusters. It rarely forms single, well-developed crystals.

Geological environment

## Genesis Murunskite is a hydrothermal mineral associated with potassic metasomatism. It forms in fenites – metasomatic rocks formed by the interaction of alkaline fluids with sedimentary rocks (sandstones) in contact with intrusions of alkaline rocks, such as charoitites. ## Mineral Associations This mineral occurs in close association with other rare minerals typical of the Murun Massif. It is most often accompanied by charoite, tinaksite, aegirine, microcline, davantite, as well as other rare sulfides like jerfisherite and rasvumite. ## Localities The only confirmed and well-documented occurrence of murunskite in the world is its type locality – the Murun Massif, located on the border of Irkutsk Oblast and the Sakha Republic (Yakutia) in Russia.

Rarity

Very rare

For collectors

## Quality Criteria Specimens most valued by collectors are those showing rich clusters of murunskite flakes, forming distinct aggregates on a contrasting background, for example, on purple charoite or white quartz/microcline. Important factors are intense color, metallic luster, and the absence of damage to the delicate flakes. Due to their small size, specimens are often evaluated under a microscope. ## Popular Localities The only source of collector specimens is the Murun Massif in Russia. Specimens from this location, especially from the "Valley of Promises" (Dolina Nadezhd) vein, are the standard for this mineral.

Care and storage

## Cleaning Due to its softness and flaky structure, mechanical cleaning is highly inadvisable. Specimens should be protected from dust by storing them in sealed containers. If necessary, compressed air can be used from a safe distance. ## What to Avoid Avoid contact with water, acids, and other chemicals that may react with sulfides. The mineral is soft and easily scratched. It should be protected from impacts and abrasion. Prolonged exposure to humid air can cause oxidation and a change in appearance. ## Storage The safest way to store specimens is to place them in a padded "micromount" box or a specialized mineralogical display case. This protects the delicate flakes from damage and limits air access.

Sources

IMA Mineral List (CNMNC)