Metarossite

Chemical formula: CaV⁵⁺₂O₆(H₂O)₂

Metarossite is a very rare, hydrated calcium vanadate, forming soft, fibrous coatings and crusts of a light yellow color.

## Characteristics Metarossite is a hydrated calcium vanadate, usually occurring as soft, powdery or chalky aggregates and coatings. Less frequently, it forms fibrous or platy aggregates. Its name refers to the mineral rossite, from which it differs by a lower degree of hydration – it forms as a result of its partial dehydration. ## Physical Properties This mineral is extremely soft, with a Mohs hardness of only 1-2, meaning it can be scratched with a fingernail. It is translucent and characterized by a dull or earthy luster. Due to its nature, its density has not been precisely determined. ## Colors and Varieties Metarossite occurs in shades from very light yellow to pale greenish-yellow. In transmitted light, it is colorless to pale yellow. No distinct color varieties or commercial forms are recognized. ## History and Name Metarossite was first described in 1927 by William F. Foshag and Frank L. Hess. Its name comes from the Greek word "meta" (changed) and the name of the mineral rossite, reflecting its genesis through the dehydration of rossite. The type locality is Arrowhead Tunnel in San Miguel County, Colorado, USA.

Properties

Mohs hardness
1-2
Luster
Dull
Density
0
Transparency
Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Metarossite can be identified by its exceptional softness (hardness 1-2), light yellow color, and occurrence as powdery, earthy, or fibrous coatings on vanadium-rich sedimentary rocks. It reacts with water. ## Distinguishing from Similar Minerals It can be confused with other secondary vanadium minerals, such as carnotite, tyuyamunite, or pascoite. Differentiation often requires chemical analysis (XRD, EDS). From rossite, from which it forms, it differs by a lower water content, a feature impossible to verify visually. ## Crystal Forms Crystals are extremely rare and appear as tiny plates or fibers. It typically forms microcrystalline, earthy, or powdery coatings and crusts.

Geological environment

## Genesis Metarossite is a secondary vanadium mineral, forming in the oxidation zones of uranium-vanadium deposits, which occur in sedimentary rocks, mainly sandstones. It forms in dry climatic conditions as a result of partial dehydration of the mineral rossite. ## Mineral Associations It often co-occurs with other vanadate minerals, such as rossite, pascoite, hewettite, as well as gypsum and calcite. ## Localities The most important occurrences of metarossite are in the USA, in the Colorado Plateau region (Colorado, Utah, Arizona states). The type locality is Arrowhead Tunnel in San Miguel County, Colorado.

Rarity

Very rare

For collectors

## Quality Criteria Metarossite specimens are valued primarily for their scientific importance and rarity. The most desirable samples are those with clearly visible, rich coatings of intense color, originating from classic localities. Due to its nature, "purity" or "crystal form" are not typical evaluation criteria. The richness of the coating and its aesthetic arrangement on the matrix rock are key. ## Popular Localities The most prized specimens come from historical uranium and vanadium mines on the Colorado Plateau in the USA, especially from the type locality in San Miguel County, Colorado.

Care and storage

## Cleaning Metarossite specimens are extremely delicate and sensitive to water. Mechanical cleaning is highly inadvisable. The safest method is to very carefully remove dust using a soft brush or a photographic blower. ## What to Avoid Contact with water and other liquids, which can dissolve or damage the mineral, must be absolutely avoided. It is sensitive to changes in humidity, which can cause further dehydration or rehydration. It should be protected from high temperatures, direct sunlight, and chemicals. ## Storage Metarossite requires storage under stable conditions. It is best kept in a closed, airtight container (e.g., a "membrane box") away from sources of moisture and temperature fluctuations to prevent further transformations.

External references

Sources

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