Metamunirite

Chemical formula: NaV⁵⁺O₃

Metamunirite is a rare, anhydrous sodium vanadate, forming white or cream-colored, fibrous coatings and aggregates.

## Characteristics Metamunirite is an anhydrous sodium vanadate, closely related to munirite, from which it differs by the absence of crystal water. It occurs as very fine, fibrous crystals, which usually form clusters, coatings, or crusts on host rocks. Individual crystals are too small to be seen with the naked eye, and aggregates have a chalky, earthy, or felt-like appearance. ## Physical Properties Metamunirite crystals are flexible and pliable. This mineral exhibits strong fluorescence under ultraviolet light, glowing yellow-green in both short-wave and long-wave UV. ## Colors and Varieties Metamunirite is typically white, cream, or very pale yellow. No color or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition and its relationship to munirite (NaVO₃·2H₂O). The prefix "meta-" indicates its anhydrous nature relative to hydrated munirite. It was first described by Howard T. Evans Jr. in 1991 based on material from several localities in the USA. ## Applications Due to its rarity and microscopic crystal size, metamunirite has no industrial applications. It is solely an object of interest for collectors specializing in rare or fluorescent minerals.

Properties

Mohs hardness
2
Color
Colourless
Luster
Silky
Streak
White
Density
2.877
Cleavage
{101} and {001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification A key diagnostic feature of metamunirite is its appearance as white, felt-like or fibrous coatings. The most important test, however, is its strong, yellow-green fluorescence under UV light. Final confirmation requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Munirite is visually indistinguishable, but it is a hydrated mineral and loses water, transforming into metamunirite upon heating. Other white, efflorescent sulfate or carbonate minerals (e.g., gypsum, epsomite) typically do not exhibit such intense fluorescence and have different physical properties. ## Crystal Forms Metamunirite forms microscopic, acicular or bladed crystals, elongated along the crystallographic axis. These crystals interweave into dense, felt-like aggregates, forming coatings and crusts.

Geological environment

## Genesis Metamunirite is a secondary mineral, formed by the weathering of vanadium-rich sedimentary rocks, such as sandstones and mudstones. It forms in desert and arid conditions as a product of dehydration of primary munirite. It occurs on rock surfaces, in fissures, and on the walls of old mine workings as an efflorescence. ## Mineral Associations It co-occurs with other secondary vanadium minerals, such as munirite, pascoite, huemulite, as well as with gypsum and calcite. ## Localities The most important localities are in the USA, in states such as Utah (e.g., San Rafael district), Colorado, Arizona, and New Mexico. This mineral is characteristic of the arid regions of the Colorado Plateau.

Rarity

Rare

For collectors

## Quality Criteria For collectors, the abundance and purity of the metamunirite coating on the rock matrix are most important. Specimens with intensely colored, dense clusters are more valued. Contrast with dark host rock enhances visual appeal. Due to the nature of the mineral, single, well-formed crystals do not occur – the quality of the entire aggregate is assessed. A strong reaction to UV light is highly desirable.

Care and storage

## Cleaning Metamunirite specimens are extremely delicate. Mechanical cleaning and contact with water should be avoided. If necessary, a very gentle stream of compressed air can be used to remove dust. ## What to Avoid Absolutely avoid contact with water and other liquids, which can dissolve or damage the delicate, fibrous crystals. Avoid vibrations, shocks, and touching the surface of the coatings, as they are very fragile. ## Storage It is recommended to store specimens in sealed, stable containers (e.g., "micromount" type) to protect them from mechanical damage, dust, and moisture. Avoid areas with high air humidity.

External references

Sources

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