Cupromolybdite

Chemical formula: Cu²⁺₃O(Mo⁶⁺O₄)₂

Cuprumolybdite is a rare copper molybdate with a honey-yellow to brown color, occurring as small, platy crystals in volcanic fumaroles.

## Characteristics Cuprumolybdite is a rare mineral from the molybdate group, chemically classified as a copper oxymolybdate. It forms very small, platy or tabular crystals that rarely exceed fractions of a millimeter. They typically occur as radial or tangled aggregates, as well as thin coatings and crusts on volcanic rocks. Its characteristic feature is an intense, honey-yellow to chestnut-brown color. ## Physical Properties This mineral is relatively soft, with a hardness of 3 on the Mohs scale. The crystals exhibit a luster described as adamantine to resinous. It is a translucent mineral. Its density is quite high, approximately 4.51 g/cm³. ## Colors and Varieties Cuprumolybdite occurs in shades ranging from bright yellow, through honey-yellow, to chestnut and dark brown. No distinct varieties have been identified. ## History and Name The name cuprumolybdite directly refers to its chemical composition – the presence of copper (Latin: *cuprum*) and molybdenum. It was first described in 2012 based on material found in the Yadovitaya fumarole on Tolbachik volcano (Kamchatka, Russia), which is its type locality. ## Uses Due to its extreme rarity and microscopic crystal size, cuprumolybdite has no industrial applications. It is solely an object of scientific interest and a collector's item for specialized collectors of rare minerals and micromounts.

Properties

Mohs hardness
3
Luster
Adamantine, Resinous
Streak
Yellow or light brown
Density
4.512
Fracture
Irregular/Uneven,Splintery
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Cuprumolybdite is identified based on its unique occurrence environment (volcanic fumaroles), characteristic honey-yellow to brown color, specific crystal habit (small, platy aggregates), and co-occurrence with other rare fumarolic minerals. The streak is yellow to light brown. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD) or spectroscopy. ## Distinguishing from Similar Minerals It can be confused with other secondary, yellow or brown molybdenum and copper minerals. It differs from the more common wulfenite by its significantly smaller crystal size and different formation environment. From molybdofornacite and other rare molybdates, it can only be distinguished by specialized analysis. ## Crystal Forms It forms very small, thin, platy or tabular crystals, often flattened. These crystals combine into radial, stellate, or chaotically tangled aggregates, and also form thin crusts and coatings.

Geological environment

## Genesis Cuprumolybdite is a mineral of volcanic origin, formed by sublimation from volcanic gases in high-temperature fumaroles. It crystallizes directly from hot vapors rich in copper and molybdenum at temperatures of approximately 500-600°C. ## Mineral Associations This mineral co-occurs with other rare products of volcanic exhalations. In its type locality (Tolbachik volcano), it has been found in association with minerals such as tenorite, hematite, powellite, as well as rare arsenates (e.g., eriocalcite, lammerite) and sulfates (e.g., langbeinite, aphthitalite). ## Localities The only confirmed and thoroughly described occurrence of cuprumolybdite in the world is its type locality – the Yadovitaya fumarole on Tolbachik volcano on the Kamchatka Peninsula in Russia.

Rarity

Very rare

For collectors

## Quality Criteria The quality of cuprumolybdite specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates on the rock matrix. Specimens with well-formed, radial groupings of an intense, honey-yellow color, contrasting with the substrate, are most highly valued. Due to the microscopic size of the crystals, the quality of the specimen viewed under magnification is crucial. ## Popular Localities The only source of cuprumolybdite specimens is Tolbachik volcano in Kamchatka. Material from this locality is extremely rare and sought after by specialized collectors of systematic minerals and micromounts.

Care and storage

## Cleaning Cuprumolybdite specimens are extremely delicate and small. Any mechanical cleaning should be avoided. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust particles. Contact with water or other chemicals is not recommended. ## What to Avoid Contact with water, acids, detergents, and other chemical agents must be strictly avoided. The mineral is soft and brittle, so it should be protected from impacts, scratching, and vibrations. It should not be heated or exposed to sudden temperature changes. ## Storage Cuprumolybdite specimens, usually in the form of micromounts, should be stored in stable, sealed "micromount boxes" that protect them from dust, moisture, and mechanical damage. Exposure to direct sunlight should be avoided.

External references

Sources

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