Metahewettite

Chemical formula: CaV₅+₆O₁₆·₃H₂O

Metahewettite is a rare vanadium mineral, forming characteristic dark red coatings and aggregates of fine crystals.

## Characteristics Metahewettite is a hydrated calcium vanadate, typically occurring as earthy or fibrous coatings and crusts on host rocks. Less commonly, it forms aggregates of small, bladed or acicular crystals. Its most distinctive feature is its intense, dark red to reddish-brown color. ## Physical Properties Metahewettite crystals are very soft, with a Mohs hardness of 1-2. They are flexible and pliable. The luster is dull for earthy aggregates, and silky or pearly on cleavage surfaces for crystalline forms. It is a translucent to opaque mineral. ## Colors and Varieties This mineral occurs in shades from dark red to reddish-brown. No color or commercial varieties are distinguished. ## History and Name The name "metahewettite" was given in 1914 by Waldemar T. Schaller. It refers to its close relationship with hewettite and the fact that it contains less water in its structure (the prefix "meta-" indicates a lower degree of hydration). Hewettite, in turn, was named after the American geologist Donnel Foster Hewett. ## Uses Metahewettite has no industrial applications. It is solely an object of interest for collectors of rare minerals and scientists.

Properties

Mohs hardness: 1-2
Luster: Dull
Streak: Red-brown
Density: 2.94
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Metahewettite is most easily identified by its intense, dark red color, very low hardness, and characteristic occurrence as earthy or fibrous coatings. It often forms thin crusts on sandstones or shales. ## Distinguishing from Similar Minerals It can be confused with hewettite, from which it is practically impossible to distinguish visually – this requires X-ray diffraction (XRD) or chemical analysis to determine the degree of hydration. Other red secondary minerals, such as realgar or cinnabar, are usually harder and have different formation environments. ## Crystal Forms Metahewettite forms microscopic, bladed crystals, elongated in one direction, which combine into fibrous, radial, or spherulitic aggregates. Most often, however, it occurs as earthy masses and coatings.

Geological environment

## Genesis It is a secondary mineral, forming in the oxidation zones of uranium and vanadium ore deposits, mainly in sedimentary rocks such as sandstones and shales. It forms under low humidity conditions as a result of dehydration of hewettite. ## Mineral Associations It most commonly co-occurs with hewettite, carnotite, tyuyamunite, gypsum, and other rare uranyl vanadates. ## Localities The most important and classic localities for this mineral are in the United States, particularly in the Colorado Plateau region (states of Utah, Colorado, Arizona, and New Mexico). It is known, among others, from San Juan County in Utah and from mines in Paradox Valley in Colorado. It also occurs in Gabon (Mounana mine) and Argentina.

Rarity

Rare

For collectors

## Quality Criteria The most prized by collectors are specimens with well-formed, even microscopic, crystals forming radial or velvety aggregates of intense red color. Contrast with a light host rock (most often sandstone) also enhances attractiveness. Specimens in the form of coatings are much more common and less valued. ## Popular Localities Specimens from classic localities in the USA, especially from the Uravan Mineral Belt in Colorado and Utah, are considered the best. Specimens from these places, acquired during historical mining operations, are now a rarity on the market.

Care and storage

## Cleaning Metahewettite specimens are extremely delicate and fragile. They should be cleaned only with a very soft brush or carefully using compressed air to remove dust. Any contact with water or other liquids is inadvisable, as the mineral is partially soluble and can be damaged. ## What to Avoid Water, chemicals, ultrasonic cleaners, and mechanical cleaning should be absolutely avoided. The mineral is very soft, so it is easily scratched or damaged. It should be protected from moisture and high temperatures, which can lead to further dehydration. ## Storage Specimens should be stored in a dry place, preferably in a closed, padded box or display case, to protect them from dust, mechanical damage, and changes in humidity. They should not be exposed to direct sunlight.

Sources

IMA Mineral List (CNMNC)