Bariandite

Chemical formula: Al₀.₆(V₅+,V₄+)₈O₂₀·₉H₂O

Bariandite is a rare vanadium mineral characterized by its distinctive dark blue to black color and fibrous appearance.

## Characteristics Bariandite is a hydrated vanadium oxide found in the oxidation zones of uranium-vanadium deposits. It forms fibrous, acicular aggregates, or massive crusts and coatings. Its appearance is very characteristic – it typically occurs as dense, felted aggregates resembling felt or velvet, with an intense, dark blue, bluish-black, or almost black color. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 1. It has a silky or dull luster, and its thin fibers are flexible. It is opaque. The density of bariandite ranges from 2.6 to 2.7 g/cm³. ## Colors and Varieties Bariandite occurs in shades from dark blue, through bluish-black, to black. No color or commercial varieties are distinguished. ## History and Name The mineral is named in honor of Pierre Bariand (born 1933), a French mineralogist and curator of the mineral collection at the Sorbonne in Paris, in recognition of his contributions to the study of vanadium minerals. The mineral was first described in 1970 based on samples from the Mounana mine in Gabon. ## Uses Bariandite has no industrial applications. It is solely a mineral of scientific and collecting interest.

Properties

Mohs hardness: 1
Luster: Silky
Streak: Bluish-black
Density: 2.6 - 2.7
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Bariandite can be identified by its characteristic dark blue to black color, fibrous or felted aggregate form, and very low hardness. Its silky luster and occurrence in paragenesis with other vanadium minerals are also important clues. ## Distinguishing from Similar Minerals Bariandite is sometimes confused with other vanadium oxides, such as doloresite or corvusite. However, doloresite is usually brown to black and harder. Corvusite is also harder and has a more resinous or metallic luster. Final differentiation often requires chemical (EDS) or X-ray (XRD) analysis. ## Crystal Forms This mineral forms fibrous, acicular aggregates, as well as massive, earthy, or felted aggregates. It occurs as crusts and veinlets filling fractures in the host rock. It does not form well-developed, macroscopic crystals.

Geological environment

## Genesis Bariandite is a secondary mineral formed in the oxidation zones of uranium-vanadium deposits, which are found in sedimentary rocks, mainly sandstones. It forms as a result of the weathering of primary vanadium minerals under low-temperature and low-pressure conditions. ## Mineral Associations It often co-occurs with other vanadium and uranium minerals, such as carnotite, tyuyamunite, doloresite, metarossite, pascoite, as well as with gypsum, calcite, and clay minerals. ## Localities The most important and classic locality (type locality) for this mineral is the Mounana mine in Gabon. It is also known from several localities in the United States, mainly in the Colorado Plateau region (Utah, Colorado, Arizona), for example, in mines in Montrose County (Colorado) and San Juan County (Utah).

Rarity

Rare

For collectors

## Quality Criteria Specimens most valued by collectors are those with intensely blue, well-preserved, "fluffy" fibrous aggregates that create an attractive contrast with the light host rock (sandstone). The abundance of material on the matrix and the absence of damage to the delicate fibers are important. Specimens from the classic locality in Gabon are particularly sought after. ## Popular Localities The most famous and prized specimens come from the Mounana mine in Gabon. Good quality collector material is also supplied by some mines in the Uravan district on the Colorado Plateau in the USA.

Care and storage

## Cleaning Bariandite specimens are extremely delicate and fragile. Mechanical cleaning, including the use of brushes, should be avoided. If absolutely necessary, compressed air can be carefully used from a safe distance to remove loose dust. ## What to Avoid Contact with water and other liquids must be strictly avoided, as the mineral is soluble and can be destroyed. It is very sensitive to shock, pressure, and friction. It should be protected from high temperatures and direct sunlight, which can cause dehydration and structural changes. ## Storage Specimens should be stored in sealed, padded boxes or micromount containers to protect them from mechanical damage, dust, and humidity changes. It is not suitable for display in open showcases.

Sources

IMA Mineral List (CNMNC)