Hendersonite

Chemical formula: Ca₁.₃(V₅+,V₄+)₆O₁₆·₆H₂O

Hendersonite is a rare, hydrated calcium vanadate, forming aggregates of microscopic, dark green to black crystals with strong pleochroism.

## Characteristics Hendersonite is a rare, secondary vanadium mineral. It occurs as very small, bladed or fibrous crystals, which typically form rosette-like or radial aggregates and coatings on host rocks, mainly sandstones. Individual crystals are usually too small to be seen with the naked eye, and aggregates range from fibrous to almost dense. ## Physical Properties Hendersonite crystals are flexible and exhibit strong pleochroism, changing color from bluish-green to yellowish-brown depending on the viewing angle. The mineral has a hardness of approximately 2.5 on the Mohs scale and a density close to 2.77 g/cm³. The luster is vitreous to almost metallic on fresh surfaces. ## Colors and Varieties This mineral has a characteristic, very dark green to black color. In transmitted light under a microscope, it reveals its pleochroic properties. No varieties of hendersonite have been distinguished. ## History and Name The mineral is named in honor of Edward Porter Henderson (1898-1992), an American chemist and curator of the meteorite collection at the Smithsonian Institution in Washington, D.C. Hendersonite was first described in 1963 from samples collected in uranium-vanadium mines in San Juan County, Utah, and Montrose County, Colorado, USA. ## Uses Due to its rarity and microscopic crystal size, hendersonite has no industrial applications. It is solely of interest to collectors specializing in rare minerals or vanadium minerals.

Properties

Mohs hardness: 2.5
Luster: Vitreous
Streak: Brownish-green
Density: 2.77
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Hendersonite can be identified by its characteristic, dark green to black, fibrous or bladed aggregates, often with a radial structure. It occurs as coatings and crusts on sandstones in uranium-vanadium deposits. Strong pleochroism is a key diagnostic feature under the microscope. ## Distinguishing from Similar Minerals It can be confused with other dark vanadium minerals, such as montroseite or corvusite. Definitive differentiation from these minerals requires advanced analytical methods, such as X-ray diffraction (XRD), due to visual similarity and co-occurrence in the same localities. ## Crystal Forms It forms microscopic, bladed crystals elongated along one axis, which combine into radial, rosette-like, or fibrous aggregates. Single, isolated crystals are rarely found.

Geological environment

## Genesis Hendersonite is a secondary mineral, forming in the oxidation zone of uranium-vanadium deposits hosted in sandstones. It forms as a result of weathering and alteration of primary vanadium minerals, such as montroseite, under low-temperature conditions. ## Mineral Associations It most commonly co-occurs with other vanadium minerals, such as hewettite, pascoite, montroseite, corvusite, as well as gypsum and calcite. These minerals collectively form colorful coatings and efflorescences on host rocks. ## Localities The most important and classic localities for hendersonite are in the USA, on the Colorado Plateau. These include mines in San Juan County (Utah), Montrose County (Colorado), and Apache County (Arizona). Outside the USA, its occurrence has been reported in the Mounana uranium mine in Gabon.

Rarity

Rare

For collectors

## Quality Criteria For collectors, the abundance and well-formed aggregates on the rock matrix are most important. The most desirable specimens are those with distinct, radial or rosette-like aggregates of dark green crystals, contrasting with the lighter host rock. The size of the specimen and the richness of associations with other rare vanadium minerals also increase its value. ## Popular Localities The best and most prized hendersonite specimens come from the historic uranium-vanadium mines in the Uravan Mineral Belt in Utah and Colorado, USA. Specimens from these classic localities are considered the standard for this species.

Care and storage

## Cleaning Mechanical cleaning should be avoided due to the delicacy of the crystals. If necessary, a very soft brush can be used to remove dust. Water or any liquids should not be used, as the mineral is hydrated and may undergo alteration. ## What to Avoid Contact with water and chemicals must be absolutely avoided. The mineral is sensitive to changes in humidity and temperature, which can lead to its dehydration and decomposition. It should not be heated or exposed to direct sunlight. ## Storage Hendersonite specimens should be stored under stable conditions, preferably in sealed, airtight boxes (so-called "perky boxes"), which protect against dust and humidity changes. Avoid storing in areas of high humidity or where rapid temperature fluctuations occur.

Sources

IMA Mineral List (CNMNC)