Bernardevansite

Chemical formula: Al<sub>2</sub>(Se<sup>4+</sup>O<sub>3</sub>)<sub>3</sub>·6H<sub>2</sub>O

Bernardevansite is a very rare, hydrated aluminum selenite, forming colorless, prismatic crystals with a vitreous luster.

## Characteristics Bernardevansite is a mineral from the selenite group, chemically a hydrated aluminum selenite. It occurs as very small, elongated, prismatic crystals, usually not exceeding 1 mm in length. The crystals are colorless and transparent, often forming disordered aggregates or fan-shaped clusters on the surface of the host rock. Due to its size and rarity, it is a mineral of interest mainly to specialized collectors and scientists. ## Physical Properties The mineral is characterized by a vitreous luster. It is relatively soft, with a Mohs hardness of approximately 2.5. Its crystals are brittle. The calculated density is 2.71 g/cm³. ## Colors and Varieties Bernardevansite is colorless. No colored varieties or trade names are known. ## History and Name The mineral was discovered in the El Dragón mine in Antonio Quijarro Province, Bolivia. It was approved by the International Mineralogical Association (IMA) in 2017 under number IMA2017-068. The name honors Bernard Evans (born 1934), a retired professor from the Department of Earth and Space Sciences at the University of Washington, in recognition of his contributions to mineralogy and petrology. ## Uses Bernardevansite has no industrial application. Its significance is purely scientific and for collectors.

Properties

Mohs hardness
2.5
Luster
Vitreous
Streak
White
Density
2.71
Cleavage
Perfect on {010}
Fracture
Not determined
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of bernardevansite under amateur conditions is practically impossible due to the microscopic size of the crystals and its occurrence in association with other visually similar selenites. Definitive identification requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other colorless, secondary selenite minerals found in the same locality, such as chalcomenite, olsacherite, or mandarinoite. Differentiation relies solely on chemical and crystallographic analysis. ## Crystal Forms Bernardevansite forms elongated, prismatic crystals with a bladed cross-section. Crystals often occur as radial or tangled aggregates.

Geological environment

## Genesis Bernardevansite is a secondary mineral, formed in the oxidation zone of hydrothermal selenium deposits. It forms as a result of the weathering of ore minerals rich in selenium, in the presence of aluminum derived from the surrounding rocks. ## Mineral Associations This mineral co-occurs with other rare selenites. At the type locality (El Dragón mine), it was found in association with chalcomenite, mandarinoite, olsacherite, as well as penroseite and other selenides. ## Localities The only confirmed occurrence of bernardevansite in the world is the El Dragón mine, located in Antonio Quijarro Province, Potosí Department, Bolivia. This is the type locality for this mineral.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of bernardevansite specimens is assessed based on the abundance and development of microcrystals on the rock matrix. The most desirable specimens are those with visible, well-formed, transparent crystals forming aesthetic aggregates. Due to the microscopic nature of the mineral, association with other rare selenites is also crucial. ## Popular Localities The only source of specimens is the El Dragón mine in Bolivia, which is world-renowned for its exceptional and rare selenite minerals.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using compressed air to remove dust. Due to its brittleness and potential solubility in water, contact with liquids should be avoided. Washing in water, especially in ultrasonic cleaners, is unacceptable. ## What to Avoid Contact with water and chemicals must be absolutely avoided. The mineral is brittle, so it must be protected from impacts and vibrations. It should not be heated or exposed to humid air. ## Storage Bernardevansite specimens should be stored under stable, dry conditions. It is best to place them in a sealed, closable "micromount" box away from dust and humidity fluctuations.

Sources

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