Rauvite

Chemical formula: Ca(U₆+O₂)₂V₅+₁₀O₂₈·₁₆H₂O

Rauvite is a hydrated calcium uranyl vanadate, forming characteristic purplish-red coatings in uranium-vanadium deposits.

## Characteristics Rauvite is a secondary mineral from the vanadate group, chemically classified as a hydrated calcium uranyl vanadate. It occurs almost exclusively as microcrystalline, earthy, or leathery coatings and crusts on host rocks, primarily sandstones. It does not form macroscopic, well-developed crystals. Its most characteristic feature is its intense, dark, purplish-red to reddish-brown color, which distinguishes it from the gangue rock. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 1-2, meaning it can be scratched with a fingernail. It has a dull or earthy luster and is opaque, although very thin fragments may sometimes be translucent. The calculated density for rauvite is approximately 3.23 g/cm³, but its measurement is practically impossible due to its mode of occurrence. ## Colors and Varieties The dominant and virtually only color found in rauvite is a shade from dark reddish-brown to deep purplish-red. No color varieties or commercial varieties are distinguished. ## History and Name The mineral was first described in 1922 by Frank L. Hess. Its name is a syllabic blend derived from the elements comprising it: radium (RA - as a decay product of uranium), uranium (U), and vanadium (V). ## Uses Rauvite has no industrial applications. It is an object of scientific interest and is sought after by specialized collectors of uranium minerals and rare mineralogical species.

Properties

Mohs hardness: 1-2
Luster: Dull
Streak: Yellowish-brown
Density: 3.23 (obliczona)
Cleavage: None
Fracture: Earthy
Transparency: Opaque, Translucent in thin fragments
Crystal system: Monoclinic

Diagnostic features

## Identification The most important diagnostic features of rauvite are its unique purplish-red color, earthy or dull appearance, and occurrence as coatings on sandstones in association with other uranium and vanadium minerals. A key feature is its radioactivity, easily detectable with a Geiger counter. The streak is yellowish-brown. ## Distinguishing from Similar Minerals Rauvite is sometimes confused with other secondary uranyl vanadates, mainly hewettite and metahewettite. Hewettite typically has a more reddish-brown hue and rarely exhibits such an intense purple tone as rauvite. However, a definitive and certain distinction between these minerals often requires advanced studies, such as X-ray diffraction (XRD). ## Crystal Forms Rauvite occurs as microcrystalline aggregates, forming earthy, leathery, or powdery coatings and crusts. It sometimes fills the cement in sandstones. It is not observed in the form of well-developed crystals visible to the naked eye.

Geological environment

## Genesis Rauvite is a secondary mineral, formed in the oxidation zone of uranium-vanadium deposits hosted in sandstones. It forms as a result of weathering and alteration of primary uranium minerals (e.g., uraninite) and vanadium minerals (e.g., montroseite) or other secondary minerals, such as carnotite and tyuyamunite, under low temperature and pressure conditions. ## Mineral Associations This mineral often co-occurs with other secondary uranium and vanadium minerals. Its most common associations include carnotite, tyuyamunite, hewettite, metahewettite, as well as gypsum and other evaporite minerals. ## Localities The most important and classic localities for rauvite are found on the Colorado Plateau in the USA, particularly in Utah (e.g., in the San Rafael Swell area, Temple Mountain - type locality), as well as in Colorado and Arizona. These are locations of historical and active uranium-vanadium deposits.

Rarity

Not very common

For collectors

## Quality Criteria The collector's value of rauvite specimens primarily depends on the richness and surface area of the coating on the host rock. Samples with an intensely colored, thick, and uniform layer of the mineral are most prized. An additional advantage is an aesthetic composition with a contrasting host rock (usually light sandstone) and the presence of other, well-formed associated minerals. ## Popular Localities Specimens from classic localities on the Colorado Plateau in the USA, especially from mines and open pits in Emery County, Utah, are considered the best in the world. These historical localities have provided exemplary rauvite samples.

Care and storage

## Cleaning Rauvite specimens should only be dry-cleaned, using a soft brush to remove dust. Compressed air should be avoided, as it could disperse radioactive dust. ## What to Avoid **The mineral is radioactive.** Inhalation of dust and particles must be strictly avoided. Hands must be thoroughly washed after each contact with the specimen. Rauvite is very soft and brittle, so it should be protected from impacts and abrasions. Contact with water and chemicals should be avoided, as it is a hydrated mineral and may undergo changes. ## Storage Rauvite specimens must be stored in sealed, preferably transparent containers (e.g., "perky box" type), clearly marked with a radioactivity warning label. They should be kept away from areas of permanent human habitation, and also away from other minerals that could be damaged by radiation (e.g., smoky quartz, fluorite).

Sources

IMA Mineral List (CNMNC)