Corvusite

Chemical formula: (Na,Ca,K)₁-x(V₅+,V₄+,Fe₂+)₈O₂₀·₄H₂O

Corvusite is a rare vanadium mineral characterized by its distinctive blue-black color, forming compact, earthy aggregates.

## Characteristics Corvusite is a hydrated vanadium, sodium, calcium, and potassium oxide. It typically occurs as compact, dense masses with an earthy or fibrous structure, as well as coatings and efflorescences on other minerals, primarily carnotite and montroseite. It rarely forms discernible crystals, and its aggregates usually have a dull to slightly lustrous appearance. Its characteristic dark color results from the presence of vanadium in various oxidation states. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 2.5-3. It is quite brittle and has an uneven fracture. The density of corvusite ranges from 2.8 to 3.4 g/cm³, depending on its exact chemical composition and degree of hydration. It exhibits a weak, silky, or earthy luster. ## Colors and Varieties Corvusite has a very characteristic color palette. It is most often blue-black, indigo-blue, or blackish-brown. In thin fragments, it can be translucent blue or greenish-blue. There are no commercial or color varieties distinguished for this mineral. ## History and Name The mineral's name comes from the Latin word *corvus*, meaning raven, which is a direct reference to its dark, almost black color. Corvusite was first described in 1914 based on material from the Colorado Plateau in the USA, which is the classic locality for this mineral. ## Uses Due to its rarity and inconspicuous appearance, corvusite has no direct industrial application. However, it is an important object of interest for collectors specializing in vanadium minerals and is a subject of scientific research as an indicator of oxidation processes in uranium-vanadium deposits.

Properties

Mohs hardness: 2.5-3
Luster: Silky
Streak: Blue-black
Density: 2.8-3.4
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of corvusite include its characteristic blue-black or indigo color and its occurrence as compact, earthy, or fibrous masses. It often forms pseudomorphs after other vanadium minerals, especially montroseite. Its presence in the oxidation zones of uranium-vanadium deposits is also an important clue. ## Distinguishing from Similar Minerals Corvusite can be confused with other vanadium oxides, such as montroseite or doloresite. Montroseite is usually black and has a more distinct luster. Doloresite has a similar composition but a different crystal structure and is often dark brown. Accurate differentiation of these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Corvusite crystallizes in the monoclinic system, but well-formed crystals are extremely rare. It typically forms compact, earthy, fibrous, or platy aggregates. It often occurs as pseudomorphs, retaining the external shape of the crystals of the mineral it replaced (e.g., montroseite).

Geological environment

## Genesis Corvusite is a secondary mineral, forming in the oxidation zones of uranium-vanadium deposits, which occur mainly in sandstones. It forms as a result of the oxidation and hydration of primary vanadium minerals, such as montroseite, under low-temperature conditions, close to the Earth's surface. ## Mineral Associations This mineral often co-occurs with other vanadium and uranium minerals. Its most common associations include: carnotite, tyuyamunite, montroseite, hewettite, pascoite, as well as gypsum and calcite. ## Localities The most important and well-known localities for corvusite are on the Colorado Plateau in the United States, encompassing the states of Utah, Colorado, Arizona, and New Mexico. Mines in San Juan County (Utah) and Montrose County (Colorado) are particularly well-known. Occurrences have also been reported in Argentina.

Rarity

Rare

For collectors

## Quality Criteria For collectors, the most valuable specimens are those where corvusite forms distinct, rich aggregates with an intense, blue-black color. Pseudomorphs of corvusite after well-formed montroseite crystals, which retain their original, sharp shape, are particularly prized. Contrasting combinations with bright yellow carnotite also significantly enhance the visual appeal and value of the specimen. ## Popular Localities The best corvusite specimens, including classic pseudomorphs, come from historical and active uranium and vanadium mines on the Colorado Plateau in the USA. Localities such as the La Sal No. 2 mine in San Juan County, Utah, are sources of many world-class specimens of this mineral.

Care and storage

## Cleaning Corvusite is a very delicate and sensitive mineral. It should only be cleaned dry, using a soft brush to remove dust. Contact with water, especially warm water, can lead to its damage or disintegration. ## What to Avoid Contact with water and all chemicals should be strictly avoided. The mineral is sensitive to changes in temperature and humidity. It should not be heated or exposed to direct sunlight, which can cause dehydration and color change. ## Storage Corvusite specimens are best stored in dry, stable conditions, in sealed containers or display cases, to protect them from dust and humidity changes. Due to its softness, contact with harder minerals should be avoided.

Sources

IMA Mineral List (CNMNC)