Ferrodimolybdenite

Chemical formula: Fe₂+Mo₃+₂S₂-₄

Ferrodimolybdenite is an extremely rare iron and molybdenum sulfide, forming tiny, hexagonal crystals with a metallic luster.

## Characteristics Ferrodimolybdenite is a mineral from the sulfide group, chemically classified as an iron and molybdenum sulfide. It occurs as extremely small, hexagonal, tabular crystals, rarely exceeding 0.1 mm. It typically forms inclusions within other minerals, mainly molybdenite. Its appearance is inconspicuous due to its microscopic size, and identification requires advanced analytical techniques. ## Physical Properties Ferrodimolybdenite crystals exhibit a metallic luster. They are opaque. Due to the microscopic size of the crystals, many physical properties, such as hardness, density, cleavage, or fracture, have not been precisely determined. ## Colors and Varieties The mineral is black in color. No varieties are known. ## History and Name Ferrodimolybdenite was first described in 1996 by A.V. Efimov, I.V. Pekov, V.Y. Karpenko, and E.G. Ryabeva. Its name refers to its chemical composition – the presence of iron (Latin: *ferrum*) and two molybdenum atoms in its chemical formula, as well as its structural similarity to molybdenite. It was approved by the International Mineralogical Association (IMA) under number IMA1995-010.

Properties

Luster: Metallic
Streak: Black
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of ferrodimolybdenite is impossible with the naked eye and requires specialized equipment. Recognition is based on chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm the presence of iron, molybdenum, and sulfur in appropriate proportions. X-ray crystallography (XRD) is used to confirm its hexagonal crystal structure. ## Distinguishing from Similar Minerals With the naked eye or under an optical microscope, it is practically indistinguishable from other tiny, black, metallic minerals with which it co-occurs, such as molybdenite. However, molybdenite (MoS₂) is much more common, softer, has a different molybdenum-to-sulfur ratio, and does not contain iron as a key component. ## Crystal Forms It forms microscopic, hexagonal, tabular crystals.

Geological environment

## Genesis Ferrodimolybdenite is a mineral of hydrothermal origin. It forms in zones where hydrothermal solutions interact with ultramafic rocks, such as dunites. At the type locality (Uel-Ual Mountain, Russia), it was found in albite-diopside veins cutting through dunites. ## Mineral Associations This mineral co-occurs with other minerals in its formation environment. It is most commonly associated with molybdenite, pyrite, chalcopyrite, diopside, albite, phlogopite, and minerals from the serpentine group. ## Localities The only confirmed and described locality of ferrodimolybdenite occurrence in the world is its discovery site: Uel-Ual Mountain in the Inagli Massif on the Aldan Plateau, in Yakutia (Sakha Republic), Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, ferrodimolybdenite is not evaluated based on typical collector criteria such as size, color, or purity of a single crystal. The value of a specimen lies solely in its confirmed presence, documented by scientific analysis. The most valuable specimens are those from the type locality, with possibly rich aggregates of microcrystals that have been unequivocally identified. ## Popular Localities The only source of specimens is the type locality in Russia. Due to its extreme rarity, this mineral is practically unavailable on the collector's market and is almost exclusively found in the collections of scientific institutions and museums.

Care and storage

## Cleaning Due to the extremely small size of the crystals and their occurrence as inclusions in other minerals, mechanical or chemical cleaning of individual ferrodimolybdenite specimens is practically impossible and not recommended. The host specimen should be cleaned using methods appropriate for the main mineral (e.g., molybdenite), avoiding aggressive chemicals. ## What to Avoid Contact with acids and strong oxidizing agents, which can damage this sulfide, should be avoided. Ultrasonic and steam cleaning should also be avoided, as they could damage delicate crystals or their surroundings. ## Storage Specimens containing ferrodimolybdenite should be stored in stable conditions, away from moisture and chemical contaminants, preferably in a closed display box to protect them from dust and mechanical damage.

Sources

IMA Mineral List (CNMNC)