Vanarsite

Chemical formula: NaCa₁₂(As³⁺V⁵⁺₈.₅V⁴⁺₃.₅As⁵⁺₆O₅₁)₂·₇₈H₂O

Wanarsite is an extremely rare vanadium-arsenate mineral with a complex chemical composition, forming microscopic, acicular crystals.

## Characteristics Wanarsite is a very complex hydrated sodium calcium arsenate and vanadate. It occurs as extremely small, acicular or bladed crystals, which form radial aggregates or chaotic clusters. Individual crystals are usually too small to be seen with the naked eye, and their aggregates appear as delicate, fibrous tufts or coatings on the host rock. ## Physical Properties Wanarsite crystals are elastic and flexible. Due to the microscopic size of the crystals, most physical properties, such as hardness or density, have not been precisely measured and are only estimated. The luster is described as silky or dull in the case of aggregates. ## Colors and Varieties This mineral has a characteristic, bright, yellowish-orange color. No varieties are known. ## History and Name Wanarsite was discovered in the St. Jude uranium and vanadium mine in San Miguel County, Colorado (USA). It was approved as a new mineral by the International Mineralogical Association (IMA) in 2012 (IMA2012-076). Its name refers to its chemical composition – the presence of vanadium and arsenic. ## Uses Wanarsite has no industrial application. It is of purely scientific significance and is of interest to specialized collectors of rare minerals.

Properties

Mohs hardness: 2
Color: Very dark blue
Luster: Silky
Streak: Grayish blue
Density: 2.48
Cleavage: {100}
Fracture: Uneven
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Wanarsite is recognized primarily by its unique appearance – bright yellow to orange, fibrous or acicular aggregates. Key to identification is the occurrence location (uranium-vanadium mines of the Colorado Plateau) and co-occurrence with other rare secondary minerals. ## Distinguishing from similar minerals It can be confused with other secondary uranium and vanadium minerals of similar color and form, such as carnotite, tyuyamunite, or pascoite. Definitive differentiation requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD), due to the microscopic size of the crystals. ## Crystal forms It forms very fine, acicular or bladed crystals, elongated along the [100] axis. These crystals combine into radial, star-shaped aggregates, spherical clusters, or form chaotic, felted masses on rock surfaces.

Geological environment

## Genesis Wanarsite is a secondary mineral, formed in the oxidation zone of uranium-vanadium deposits in sedimentary rocks (sandstones). It forms as a result of weathering and alteration of primary ore minerals under conditions of low temperatures and pressures, in the presence of waters rich in dissolved elements. ## Mineral associations This mineral occurs in association with other rare secondary minerals, such as ansermetite, duttonite, huemulite, hughesite, pascoite, schindleryte, and montroseite. ## Localities The only confirmed locality of wanarsite in the world is its type locality – the St. Jude mine, Slick Rock district, San Miguel County, Colorado, USA.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of wanarsite specimens is assessed primarily based on the richness and aesthetics of the crystal aggregates on the host rock. The most valued specimens are those with well-formed, radial clusters of intense, yellowish-orange color, contrasting with the substrate. Due to the microscopic nature of the mineral, specimens are usually small (so-called "micromounts"). ## Popular localities The only source of wanarsite specimens is the St. Jude mine in Colorado, USA. Material from this locality is extremely limited and sought after by collectors specializing in rare mineral species or minerals from the Colorado Plateau.

Care and storage

## Cleaning Wanarsite specimens are extremely delicate and susceptible to mechanical damage. Mechanical or chemical cleaning is not recommended. Any attempts at cleaning, even with water, can destroy the fragile crystal aggregates. It is best to leave the specimen in its untouched state. ## What to avoid Contact with water, chemicals, ultrasound, and any vibrations or impacts must be strictly avoided. The mineral is sensitive to changes in humidity and temperature, which can lead to its dehydration and disintegration. ## Storage Specimens should be stored in stable conditions, in closed, padded containers (e.g., "micromount box"), to protect them from dust, humidity, and physical damage. Avoid exposure to direct sunlight.