Vanoxite

Chemical formula: V<sup>4+</sup><sub>4</sub>V<sup>5+</sup><sub>2</sub>O<sub>13</sub>·8H<sub>2</sub>O

Vanoxite is a rare vanadium oxide, forming dark, almost black coatings and aggregates in sedimentary rocks.

## Characteristics Vanoxite is a hydrated vanadium oxide, occurring as earthy or fibrous aggregates, as well as thin coatings and crusts. It typically appears massive, without visible crystals. Its appearance is inconspicuous; it often forms dark, almost black masses intergrown with the host rock. ## Physical Properties This mineral is very soft, with a Mohs hardness of approximately 2. It has a dull or earthy luster. It is opaque. Its density is difficult to measure precisely due to its mode of occurrence, but it is estimated to be around 2.83 g/cm³. ## Colors and Varieties Vanoxite has a characteristic, very dark color – from black to greenish-black. The streak of this mineral is brownish-black. No color or commercial varieties are distinguished. ## History and Name The name "vanoxite" directly refers to the mineral's chemical composition – it is a vanadium oxide. It was first described by Frank L. Hess in 1924 based on material found in the La Sal Mountains in Utah, USA. ## Uses Due to its rarity and inconspicuous appearance, vanoxite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or vanadium minerals.

Properties

Mohs hardness
2
Luster
Dull
Streak
Brownish black
Density
2.83
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Vanoxite is identified by its black or greenish-black color, earthy or dull appearance, and very low hardness. It occurs as coatings, earthy masses, or fibrous aggregates, often in association with other vanadium minerals such as carnotite. ## Distinguishing from Similar Minerals It can be confused with other black, earthy oxide minerals, such as manganese oxides (psilomelane, pyrolusite). Differentiation often requires chemical analysis to confirm the presence of vanadium. Association with bright yellow carnotite in sandstones is a strong diagnostic indicator. ## Crystal Forms Vanoxite does not form well-developed crystals. It occurs as earthy, massive, fibrous aggregates or as thin coatings and crusts on other minerals or in the cement of sedimentary rocks.

Geological environment

## Genesis Vanoxite is a secondary mineral, formed in the oxidation zone of uranium-vanadium deposits located in sedimentary rocks, mainly sandstones. It forms as a result of the weathering of primary vanadium minerals under conditions of low temperatures and pressures. ## Mineral Associations It most commonly co-occurs with carnotite, tyuyamunite, hewettite, gypsum, as well as copper minerals such as malachite and azurite. It often impregnates the sandstones in which it occurs. ## Localities The most important and classic vanoxite localities are in the USA, in the states of Utah (La Sal Mountains, Paradox Valley) and Colorado (Uravan region). It is also known from several locations in Arizona. These are the main sources of specimens of this mineral worldwide.

Rarity

Rare

For collectors

## Quality Criteria The collector appeal of vanoxite is limited due to its inconspicuous appearance. The most valued specimens are those where vanoxite forms distinct, rich aggregates of an intensely black color. Samples showing its clear association with contrasting minerals, especially bright yellow carnotite, are particularly sought after. The quality of a specimen depends on the abundance of the mineral on the rock matrix and the absence of damage to the delicate aggregates. ## Popular Localities The vast majority of collector specimens come from historical uranium and vanadium mines in the Uravan Mineral Belt region in Colorado and Utah, USA. Specimens from these classic localities are most desired by collectors specializing in mineral systematics.

Care and storage

## Cleaning Vanoxite specimens are extremely delicate and fragile. Mechanical cleaning should be avoided. If absolutely necessary, a very soft brush can be used to remove loose dust. Water or any chemicals should not be used, as this may damage or dissolve the mineral. ## What to Avoid Contact with water, acids, detergents, and other cleaning agents must be strictly avoided. The mineral is very soft, so it must be protected from scratching and impacts. It should not be heated or exposed to ultrasound. ## Storage Vanoxite specimens are best stored in closed, padded collector boxes to protect them from mechanical damage, dust, and moisture. Storage in a humid environment should be avoided.

Sources

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