Phosphovanadylite-Ca

Chemical formula: CaV<sup>4+</sup><sub>4</sub>P<sub>2</sub>O<sub>10</sub>(OH)<sub>6</sub>·12H<sub>2</sub>O

Phosphovanadylite-Ca is a rare secondary mineral, forming characteristic blue-green, spherical aggregates and radial clusters.

## Characteristics Phosphovanadylite-Ca is a hydrated vanadium and calcium phosphate, occurring in the oxidation zones of uranium-vanadium deposits. It forms characteristic spherical aggregates with a radial structure, reaching up to 2 mm in diameter. These are composed of very fine, lath-like or acicular crystals. Specimens typically have an intense, blue-green color. ## Physical Properties Crystals are elastic and flexible. The mineral exhibits weak, greenish-yellow fluorescence under ultraviolet light (both longwave and shortwave). Its Mohs hardness is approximately 2.5, and its density is close to 2.45 g/cm³. The luster is vitreous to pearly on cleavage surfaces. ## Colors and Varieties This mineral occurs in shades from blue-green to grayish-green. No varieties have been distinguished. ## History and Name Phosphovanadylite-Ca was first described in 2012 by Travis A. Olds and co-workers. Its name refers to its chemical composition – the presence of phosphorus (phospho-), vanadium (-vanadyl-), and the dominant cation, which is calcium (-Ca). The name was approved by the International Mineralogical Association (IMA).

Properties

Mohs hardness
2.5
Luster
Vitreous to pearly
Streak
Light green
Density
2.45
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features include its occurrence as small, radial, spherical aggregates, intense blue-green color, and specific geological environment (oxidation zones of U-V deposits). ## Distinguishing from Similar Minerals It can be confused with other secondary vanadium minerals, such as minasragrite or szymanskiite, but it differs from them in crystal habit and precise chemical composition, which requires advanced analyses (e.g., XRD, EDS). ## Crystal Forms It forms spherulitic (spherical) aggregates with an internal radial structure, composed of fine, lath-like crystals elongated along the [010] axis and flattened parallel to {001}.

Geological environment

## Genesis It is a secondary mineral, formed as a result of weathering processes in the oxidation zones of sedimentary uranium-vanadium deposits. It crystallizes from aqueous solutions under low-temperature conditions. ## Mineral Associations It co-occurs with other secondary minerals such as gypsum, minasragrite, orthominasragrite, szymanskiite, as well as montmorillonite and quartz. ## Localities The only confirmed occurrence of this mineral (type locality) is the Blue Cap uranium and vanadium mine in San Juan County, Utah, USA.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens are those with well-formed, undamaged spherulites of intense blue-green color, clearly contrasting with the host rock. Due to the microscopic size of the crystals, the quality of the entire aggregate is crucial. ## Popular Localities The only known source of specimens is the Blue Cap mine in Utah, USA, which makes them highly sought after by collectors specializing in rare minerals and "micromounts."

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to their high delicacy and solubility, contact with water and other liquids should be avoided. ## What to Avoid Water, chemicals, ultrasound, and high temperatures must be strictly avoided, as they can lead to dehydration and destruction of the mineral. Fragile aggregates are very sensitive to any shocks and touch. ## Storage It is recommended to store specimens in closed, stable containers (e.g., "micromount boxes") to protect them from mechanical damage, dust, and humidity changes. Exposure to direct sunlight should be avoided.

Sources

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