Meta-ankoleite

Chemical formula: K(U<sup>6+</sup>O<sub>2</sub>)(PO<sub>4</sub>)·3H<sub>2</sub>O

Meta-ankoleite is a rare, radioactive secondary mineral of the uranyl phosphate group, forming characteristic yellow coatings and small, tabular crystals.

## Characteristics Meta-ankoleite is a hydrated potassium uranyl phosphate, belonging to the autunite group. It forms characteristic thin crystals with a square outline and tabular habit, often arranged in fan-shaped or rosette aggregates. It also occurs as micaceous aggregates, earthy masses, or as coatings and crusts on other minerals and rocks. Its most recognizable feature is its intense yellow to greenish-yellow color. This mineral exhibits strong green fluorescence under ultraviolet light. ## Physical Properties It is a very soft mineral, with a hardness of about 2 on the Mohs scale, making it susceptible to scratching. It has a vitreous to waxy luster, and on perfect cleavage surfaces, it is pearly. It is transparent to translucent. Despite its fragility, it is characterized by a relatively high density (approximately 3.99 g/cm³), which is typical for uranium-bearing minerals. ## Colors and Varieties The color of meta-ankoleite is uniform and ranges from lemon-yellow to greenish-yellow. No color varieties or commercial varieties are distinguished. ## History and Name The mineral was first described in 1966. Its name refers to the lower water content ("meta") in its structure compared to the hypothetical, fully hydrated "ankoleite" (which was discovered later). The name "ankoleite" comes from the type locality – the Ankole District in Uganda. ## Uses Meta-ankoleite, like other secondary uranium minerals, is primarily of scientific and collector's interest. It can be a minor component of uranium ores, but it rarely occurs in concentrations that allow for profitable exploitation.

Properties

Mohs hardness
2
Luster
Vitreous, Waxy, Pearly
Streak
Pale yellow
Density
3.99
Cleavage
Perfect on {001}
Transparency
Transparent to Translucent
Crystal system
Tetragonal

Diagnostic features

## Identification Key diagnostic features of meta-ankoleite are its intense yellow color, tabular crystal form, perfect cleavage in one direction, and strong green fluorescence under UV light. Its high density is also helpful in identification. ## Distinguishing from Similar Minerals Meta-ankoleite is visually almost identical to other minerals of the autunite group, such as autunite, meta-autunite, or uranocircite. Definitive differentiation usually requires advanced analytical methods, such as X-ray diffraction (XRD). Autunite tends to be more greenish and may exhibit more intense fluorescence. Carnotite, also yellow, usually has a more earthy or dull luster and does not show such strong fluorescence. ## Crystal Forms Crystals are thin, tabular, with a square or rectangular outline. They usually form fan-shaped, radial, or rosette aggregates. They often occur as coatings composed of microscopic, platy crystals, giving the surface a pearly luster.

Geological environment

## Genesis Meta-ankoleite is a secondary mineral, formed in the oxidation (weathering) zones of uranium deposits. It forms as a result of groundwater containing phosphates acting on primary uranium minerals, such as uraninite. It most commonly occurs in fractures and on the surfaces of sedimentary rocks (mainly sandstones) and in altered granites and pegmatites. ## Mineral Associations It often co-occurs with other secondary uranium minerals, such as autunite, torbernite, phosphuranylite, as well as with gypsum, limonite, and primary uraninite. ## Localities The most important occurrences of this mineral are the Mounana mine in Gabon, which has yielded some of the world's best specimens. It is also known from the type locality in the Ankole District in Uganda, as well as from numerous locations on the Colorado Plateau in the USA (Utah, Colorado, Arizona) and from the Lake Boga area in Victoria, Australia.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals of intense, lemon-yellow color. Rich crystalline aggregates forming striking rosettes or fans on a contrasting rock matrix are also highly valued. Due to the small size of the crystals, any specimen with visible, undamaged forms is considered valuable. ## Popular Localities The Mounana mine in Gabon is considered classic and provides the best quality specimens. Specimens from there are characterized by exceptionally well-formed crystals. Numerous finds also come from the Morrison Formation sandstones on the Colorado Plateau in the USA, although specimens from there more often take the form of coatings and crusts.

Care and storage

## Cleaning Meta-ankoleite specimens should only be dry-cleaned, using a soft brush to remove dust. Avoid contact with water, which can affect the mineral's hydration state and structure. ## What to Avoid The mineral is highly radioactive. Direct contact should be minimized, and hands should be thoroughly washed after each handling of the specimen. Meta-ankoleite is very soft and brittle, so it must be protected from impacts, shocks, and friction. As a hydrated mineral, it is sensitive to high temperatures and changes in humidity, which can lead to its dehydration and disintegration. ## Storage Due to its radioactivity, specimens should be stored in tightly sealed, lead or glass containers, away from areas of permanent human presence. The container must be clearly marked as radioactive material. It should not be stored near other minerals that may be sensitive to radiation (e.g., smoky quartz, amethyst, fluorite).

Sources

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