Pandoraite-Ba

Chemical formula: BaV<sup>4+</sup><sub>5</sub>V<sup>5+</sup><sub>2</sub>O<sub>16</sub>·3H<sub>2</sub>O

A very rare hydrated barium vanadate, forming aggregates of black, bladed crystals on sandstone.

## Characteristics Pandoraite-Ba is a hydrated vanadium and barium oxide, belonging to the pandoraite group. It forms microscopic, bladed or platy crystals, which typically arrange into dense, felted or radial aggregates. Specimens appear as thin coatings and crusts or fillings of small fractures in the host rock, which is sandstone. Individual crystals are too small to be observed with the naked eye. ## Physical Properties Pandoraite-Ba crystals are soft, with a hardness of about 2.5 on the Mohs scale. The mineral exhibits a submetallic or somewhat greasy luster. It is opaque. Its density, calculated from the formula and cell parameters, is approximately 3.65 g/cm³. ## Colors and Varieties This mineral occurs in a uniform, black or brownish-black color. No color varieties or commercial varieties are known. ## History and Name Pandoraite-Ba was first described in 2011 by Anthony R. Kampf and his team. The name refers to the discovery locality, the Pandora mine in La Sal, San Juan County, Utah (USA). The "-Ba" suffix indicates that it is a barium-dominant analog of pandoraite.

Properties

Mohs hardness
2.5
Luster
Sub-metallic
Streak
Brownish-black
Density
3.65
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of pandoraite-Ba include its black color, bladed crystal habit forming felted aggregates, and occurrence as coatings on sandstone. Its origin from the only known locality is also crucial. ## Differentiation from Similar Minerals It can be confused with other black vanadium minerals found in the same environment, such as montroseite, corvusite, or doloresite. Distinguishing it based on visual characteristics is very difficult and usually requires advanced analytical methods, such as chemical analysis (EDS) or X-ray diffraction (XRD). ## Crystal Forms It forms aggregates of felted, bladed, or fibrous crystals. The crystals are elongated and flattened, reaching lengths of up to several tens of micrometers.

Geological environment

## Genesis Pandoraite-Ba is a secondary mineral. It forms in the oxidation zone of uranium-vanadium deposits in sandstones. Its crystallization occurs at low temperatures as a result of the alteration of earlier ore minerals under the influence of formation waters. ## Mineral Associations This mineral coexists with other rare vanadates. At the type locality, it was found in association with ansermetite, barnesite, corvusite, hewettite, montroseite, and paramontroseite. All occur on a sandstone matrix. ## Localities The only confirmed occurrence of pandoraite-Ba in the world is the Pandora mine, located in the La Sal area of San Juan County, Utah, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, pandoraite-Ba is primarily valued by collectors specializing in rare species and "micromount" specimens. The most highly rated specimens are those with rich, well-formed crystal aggregates covering a significant surface area of the matrix. The presence of well-identified associated minerals is also valuable. ## Popular Localities All known collector specimens come from the type and only locality - the Pandora mine in Utah, USA.

Care and storage

## Cleaning Specimens should only be dry-cleaned, using compressed air to remove dust. Due to the softness and delicate structure of the aggregates, any mechanical contact, including with brushes, should be avoided. ## What to Avoid The mineral is very susceptible to mechanical damage. Contact with water and all chemicals, as well as ultrasonic cleaners, must be strictly avoided. As a hydrated mineral, it may dehydrate at elevated temperatures. ## Storage It is recommended to store specimens in sealed micromount containers to protect them from dust, moisture, and physical damage. Avoid exposure to direct sunlight and extreme temperatures.

Sources

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