Shadlunite

Chemical formula: (Fe,Cu)<sub>₈</sub>(Pb,Cd)S<sub>₈</sub>

Shadlunite is a rare iron, copper, and lead sulfide, forming fine, metallic grains in volcanic rocks.

## Characteristics Shadlunite is a rare mineral from the sulfide group, chemically classified as an iron, copper, and lead sulfide, with possible cadmium admixture. It occurs as very small, irregular grains or intergrown aggregates, rarely exceeding 0.5 mm. Its appearance is typically metallic, and its color ranges from brownish-pink to light brown. It is usually observed in polished sections under a microscope, where it reveals its subtle optical properties. ## Physical Properties This mineral is characterized by a metallic luster. It is opaque. Due to the small size of the grains, precise determination of hardness and density is difficult; however, its hardness is estimated at approximately 4 on the Mohs scale. It does not exhibit cleavage, and its fracture is uneven. ## Colors and Varieties In fresh fracture, shadlunite has a brownish-pink to light brown color. No color varieties or commercial varieties are distinguished. ## History and Name The mineral is named in honor of Tatiana Nikolaevna Shadlun (1912-1995), a Russian mineralogist and researcher of ore deposits from the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM) in Moscow. It was approved as a new mineral by the IMA in 1973. ## Uses Shadlunite has no industrial application. Its significance is purely scientific and collectible, as a rare component of certain types of sulfide deposits.

Properties

Mohs hardness: 4
Luster: Metallic
Streak: Black
Density: 4.4-4.6
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identifying shadlunite is extremely difficult and practically impossible without advanced laboratory techniques. Identification relies on chemical analysis (e.g., using an electron microprobe) and optical studies in reflected light on polished sections. Its characteristic brownish-pink color and co-occurrence with other sulfides in a specific geological environment are key indicators. ## Distinguishing from Similar Minerals Under the microscope, shadlunite can be confused with other sulfides of similar color, such as pentlandite or cubanite. Differentiation requires precise chemical analysis, as optical properties can be very similar. ## Crystal Forms Shadlunite forms exclusively anhedral (irregularly shaped), irregular grains and aggregates, often as inclusions in other sulfide minerals such as chalcopyrite, cubanite, or pentlandite. It is not observed in the form of well-developed crystals.

Geological environment

## Genesis Shadlunite is a hydrothermal mineral, associated with volcanic processes. It forms in copper and nickel sulfide deposits that have undergone metamorphism. It occurs in paragenesis with other sulfides within volcanic and volcaniclastic rocks. ## Mineral Associations This mineral most commonly co-occurs with chalcopyrite, cubanite, pentlandite, magnetite, troilite, as well as rarer minerals such as djerfisherite, talnakhite, and mackinawite. ## Localities The most important and well-documented occurrences of shadlunite worldwide are the copper-nickel deposits in the Norilsk region of Siberia, Russia, particularly in the Mayak and Komsomolsky mines (type locality). Its presence has also been noted in the Duluth igneous complex in Minnesota (USA).

Rarity

Very rare

For collectors

## Quality Criteria The quality of a shadlunite specimen is determined not by the mineral itself, which is microscopic, but by the richness and quality of the entire mineral association. The most desirable samples are from known localities (Norilsk) where shadlunite occurs in association with well-formed crystals of other rare sulfides. Confirmation of shadlunite's presence through analysis is crucial for the scientific and collectible value of the specimen. ## Popular Localities The only source of specimens of collectible significance is the Norilsk region in Russia. Specimens from these historic deposits are highly valued by collectors specializing in rare minerals and systematics.

Care and storage

## Cleaning Due to its extreme rarity and small grain size, shadlunite specimens usually occur as inclusions in other minerals and do not require cleaning. Any cleaning of the host rock should be done with the utmost care, preferably mechanically, using a soft brush and compressed air, to avoid damaging the delicate grains. ## What to Avoid Contact with chemicals, especially acids, which can react with sulfides, should be avoided. Specimens should also be protected from moisture, which can accelerate oxidation processes and dulling of the mineral's surface. ## Storage Specimens containing shadlunite should be stored in stable conditions, in a dry environment, away from direct sunlight and sources of chemical contamination. It is best to keep them in closed collector boxes or display cases.

Sources

IMA Mineral List (CNMNC)