Bicapite

Chemical formula: [KNa<sub>2</sub>Mg<sub>2</sub>(H<sub>2</sub>O)<sub>25</sub>][H<sub>2</sub>PV<sup>5+</sup><sub>12</sub>O<sub>40</sub>(V<sup>5+</sup>O)<sub>2</sub>]

Bicapite is an extremely rare mineral from the vanadate group, forming microscopic, black crystals with a metallic luster.

## Characteristics Bicapite is a very complex hydrated potassium, sodium, and magnesium vanadate. It occurs as extremely small, tabular or bladed crystals, rarely exceeding 0.2 mm in length. Observed under a microscope, they form fan-shaped or radial aggregates. It is an opaque mineral with a black color and metallic luster. ## Physical Properties Bicapite crystals are too small to accurately determine their hardness or density using standard methods. The density was calculated based on the chemical formula and unit cell parameters, and is approximately 2.45 g/cm³. The luster is described as metallic. ## History and Name The mineral's name comes from two Latin words: *bi-* (two) and *caput* (head), referring to its crystal structure containing two distinct, interconnected polyoxovanadate clusters. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2014 (IMA2014-014). It was described by a team of mineralogists led by Anthony R. Kampf based on specimens from the Blue Cap uranium mine in San Juan County, Utah, USA.

Properties

Luster
Metallic
Streak
Black
Density
2.45
Cleavage
Perfect on {100}
Transparency
Opaque
Crystal system
Triclinic

Diagnostic features

## Identification Identification of bicapite is impossible without advanced laboratory techniques, such as X-ray diffraction (XRD) and chemical microanalysis (EDS). In collector conditions, identification relies solely on trust in the label from a reputable source that has confirmed analytical identification. Visually, they are simply microscopic, black crystals. ## Distinguishing from Similar Minerals Bicapite can be visually indistinguishable from many other rare, black secondary minerals found in uranium-vanadium deposits, such as ansermetite, lasalite, nashite, or schindlerite. Definitive differentiation is only possible through chemical and structural analysis. ## Crystal Forms Bicapite forms very small, thin, tabular or bladed crystals, often flattened. They typically occur as radial or fan-shaped aggregates and clusters on the surface of the host rock.

Geological environment

## Genesis Bicapite is a secondary mineral that forms in the oxidation zone of uranium-vanadium deposits in sedimentary rocks (sandstones). It crystallizes post-mining on the walls of mine workings as a result of the evaporation of mine waters rich in vanadium, potassium, sodium, and magnesium in an arid climate. ## Mineral Associations This mineral co-occurs with other rare vanadates, such as ansermetite, lasalite, nashite, schindlerite, as well as gypsum and montmorillonite. ## Localities The only confirmed locality for bicapite in the world is its type locality – the Blue Cap uranium mine, located on the La Sal Plateau in San Juan County, Utah, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a bicapite specimen primarily depends on the richness and aesthetics of the microcrystal aggregates on the rock matrix. The most valued specimens are those where crystals form distinct, radial or fan-shaped clusters, well-separated from other minerals. Due to their microscopic nature, the quality of the accompanying microphotograph is crucial. ## Popular Localities All known bicapite specimens originate exclusively from the Blue Cap mine in Utah, USA. This is the only place where this mineral has been found to date.

Care and storage

## Cleaning Due to its extreme rarity, small crystal size, and delicacy, bicapite specimens should not be cleaned mechanically or chemically. Any attempts at cleaning risk irreversible destruction of the mineral. They should be left undisturbed on their original rock matrix. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and sudden temperature changes. The crystals are brittle and sensitive to any vibrations and impacts. Specimens should not be exposed to direct sunlight. ## Storage Bicapite specimens require storage under stable conditions, preferably in a closed, padded "micromount" box, which protects them from dust, moisture, and mechanical damage. Display should only take place in a controlled environment.

Sources

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