Kegginite

Chemical formula: Pb²⁺₃Ca₃[As⁵⁺V⁵⁺₁₂O₄₀(V⁵⁺O)]·₂₀H₂O

Kegginite is a very rare, orange-red arsenate-vanadate with a complex structure, forming tiny, hexagonal crystals.

## Characteristics Kegginite is a complex, hydrated lead and calcium arsenate-vanadate. It occurs as very small, hexagonal, tabular crystals, rarely exceeding 0.2 mm. It also forms rosette aggregates and thin coatings on the host rock. Its most distinctive feature is its intense, orange-red color. ## Physical Properties This mineral is very soft, with a Mohs hardness of 2. It has a density of 2.69 g/cm³. The crystals are transparent and exhibit a vitreous luster. Due to the small size of the crystals, most physical properties are difficult to observe without magnification. ## Colors and Varieties Kegginite occurs in a uniform, orange-red color. No color varieties or commercial forms are known. ## History and Name The name "kegginite" refers to the mineral's molecular structure, which is based on the so-called Keggin ion – a type of polyoxometalate characteristic of heteropolyacids. The mineral was first described in 2016 based on material from the Packrat Mine in Colorado, USA. ## Uses Kegginite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and scientists studying vanadium mineralogy.

Properties

Mohs hardness: 2
Luster: Vitreous
Streak: Pinkish-orange
Density: 2.69
Cleavage: on {001}
Fracture: Irregular/Uneven
Transparency: Transparent
Crystal system: Trigonal

Diagnostic features

## Identification Kegginite can be identified by its characteristic orange-red color, hexagonal outline of small crystals, and occurrence in paragenesis with other secondary vanadium minerals. A pinkish-orange streak is also a diagnostic feature. However, final identification requires advanced analytical methods. ## Distinguishing from Similar Minerals It can be confused with other orange or red secondary minerals, such as carnotite or tyuyamunite, which often co-occur in the same localities. Kegginite differs from them in crystal habit (hexagonal tablets) and specific mineral paragenesis. Unlike carnotite, it is not radioactive. ## Crystal Forms The mineral forms very small, thin, tabular crystals with a hexagonal outline. These crystals often group into rosette or radial aggregates. It also occurs as thin coatings and efflorescences.

Geological environment

## Genesis Kegginite is a secondary mineral, forming in the oxidation zones of uranium-vanadium deposits in sedimentary rocks, mainly sandstones. It forms as a result of the weathering of primary vanadium minerals under low-temperature conditions. ## Mineral Associations This mineral co-occurs with other secondary vanadium and uranium minerals. It is most commonly associated with: carnotite, tyuyamunite, hewettite, metahewettite, as well as gypsum, barite, and calcite. ## Localities The only confirmed and typical locality for kegginite is the Packrat Mine, located in the Beaver Mesa area (Gateway Mining District) in Mesa County, Colorado, USA.

Rarity

Very rare

For collectors

## Quality Criteria As a "micromount" type mineral, specimens with well-formed, sharp crystals of intense, orange-red color, forming aesthetic aggregates, are most highly valued. The contrast with the host rock and the presence of associated minerals are also important. Due to its extreme rarity, every well-identified specimen is valuable. ## Popular Localities The only source of kegginite specimens is its type locality – the Packrat Mine in Colorado, USA. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Kegginite specimens are extremely delicate and small. Any mechanical cleaning, including the use of brushes, should be avoided. If absolutely necessary, compressed air can be used from a safe distance to remove dust. Contact with water, especially deionized water, can damage the mineral. ## What to Avoid Contact with water, acids, and other chemicals must be strictly avoided. The mineral is very soft and susceptible to mechanical damage. It should be protected from high temperatures, which can lead to dehydration and structural destruction. ## Storage Specimens should be stored under stable conditions, in closed, padded "micromount" boxes to protect them from dust, moisture, and physical damage. They should not be exposed to direct sunlight.