Caseyite
Chemical formula: [(V<sup>5+</sup>O<sub>2</sub>)Al<sub>7.5</sub>(OH)<sub>15</sub>(H<sub>2</sub>O)<sub>13</sub>]<sub>2</sub>[H<sub>2</sub>V<sup>4+</sup>V<sup>5+</sup><sub>9</sub>O<sub>28</sub>][V<sup>5+</sup><sub>10</sub>O<sub>28</sub>]<sub>2</sub>·90H<sub>2</sub>O
Caseyite is a very rare, hydrated aluminum vanadate, forming pale yellow, microscopic crystals and coatings on uranium sandstone deposits.
Properties
- Mohs hardness
- 2-3
- Luster
- Vitreous to silky
- Streak
- pale yellow streak
- Density
- 2.151
- Fracture
- Conchoidal
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Caseyite can be identified by its characteristic pale yellow color, low hardness, and occurrence as fine, bladed or acicular crystals forming rosette-like or spherical aggregates. Its association with uranium and vanadium-bearing sandstones is key. ## Distinguishing from Similar Minerals It can be confused with other secondary vanadium minerals, such as carnotite or tyuyamunite, which often co-occur in the same localities. Distinguishing it requires advanced analytical methods, such as X-ray diffraction (XRD), due to the microscopic size of the crystals. Field identification is practically impossible. ## Crystal Forms Caseyite crystals are very small, typically less than 0.1 mm in length. They take the form of thin, flattened blades or needles. They combine into characteristic, spherical or hemispherical aggregates with a radial internal structure, as well as clusters resembling rosettes or fans.
Geological environment
## Genesis Caseyite is a secondary mineral, formed in the oxidation zone of "roll-front" type uranium-vanadium deposits, which occur in sedimentary rocks, mainly sandstones. It forms as a result of weathering and alteration of primary uranium and vanadium minerals under low temperature and pressure conditions. ## Mineral Associations This mineral occurs in association with other secondary vanadate and uranium minerals. The most commonly associated minerals are: metarossite, pascoite, sherwoodite, as well as montmorillonite, quartz, and calcite. ## Localities Caseyite is an extremely rare mineral, known only from a few localities worldwide, all located on the Colorado Plateau in the USA. It has been identified in the West Sunday, Packrat, and Burro Mines in Colorado and Utah.
Rarity
Extremely rare
For collectors
## Quality Criteria As a micromineral, caseyite is valued primarily for the abundance and quality of its well-formed crystals visible under magnification. The most desirable specimens feature well-formed, spherical or rosette-like aggregates of intense yellow color, clearly contrasting with the host rock. The aesthetic composition with other rare associated minerals is also important. ## Popular Localities All known and prized caseyite specimens originate from its type localities in the USA, particularly from mines in the Slick Rock, Gateway, and Gypsum Valley districts in Colorado. Specimens from these locations are the standard for this species.
Care and storage
## Cleaning Caseyite specimens should be cleaned with utmost care, using only a soft brush to remove loose contaminants. Due to its reactivity and solubility in water, contact with liquids, including distilled water and alcohol, should be avoided. ## What to Avoid The mineral is very sensitive to moisture and can be damaged or dissolved upon contact with water. It must be protected from all chemicals, acids, and detergents. It is also sensitive to heat and direct sunlight, which can lead to its dehydration and destruction. ## Storage Caseyite requires storage in a dry, stable environment. The best solution is a sealed container (a "perky box") or a display case with a desiccant. It should be kept away from sources of heat and light to prevent its degradation.