Saléeite

Chemical formula: Mg(U₆+O₂)₂(PO₄)₂·₁₀H₂O

Saléeite is a radioactive secondary mineral of the autunite group, a hydrated uranyl magnesium phosphate, forming characteristic yellow, tabular crystals.

## Characteristics Saléeite is a mineral belonging to the autunite group, chemically classified as a hydrated uranyl magnesium phosphate. It forms thin, tabular crystals with a square or rectangular outline, which often arrange into fan-shaped aggregates, rosettes, or form scaly crusts on the host rock. Its most characteristic feature is its intense, lemon-yellow to yellowish-green color. This mineral exhibits strong, yellowish-green fluorescence under ultraviolet light (both shortwave and longwave), which is typical for many secondary uranium minerals. ## Physical Properties Saléeite is a relatively soft mineral, with a Mohs hardness of 2-3. It has a vitreous luster, and on cleavage planes, it can be pearly. It is transparent to translucent. Its density is approximately 3.27 g/cm³. It exhibits perfect cleavage in one direction, which allows it to easily separate into thin, flexible lamellae, similar to mica. It is a highly radioactive mineral and should be handled with appropriate precautions. ## Colors and Varieties The dominant and practically sole color range for saléeite is the spectrum from pale yellow, through lemon-yellow, to yellowish-green. The intensity and hue depend on the specific location and impurities. No named color varieties or commercial names are distinguished for it. ## History and Name The mineral was first described in 1932 by Jacques Thoreau and Johannes Franciscus Vaes. Its name commemorates Achille Salée (1883-1932), a Belgian professor of geology and mineralogy at the Catholic University of Louvain. The type locality, from which the first described specimens originated, is the Shinkolobwe mine in the Democratic Republic of Congo. ## Uses Due to its rarity, saléeite has no industrial significance as a uranium ore. However, it is a valued and sought-after collector's stone, being an important subject for scientific research on secondary uranium minerals.

Properties

Mohs hardness: 2-3
Color: Lemon-yellow, straw-yellow, greenish yellow
Luster: Vitreous (Glassy)
Streak: Yellow-white
Density: 3.27
Cleavage: [001] Perfect, [010] Indistinct, [110] Indistinct
Fracture: Micaceous
Transparency: Transparent,Translucent,Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of saléeite are its characteristic lemon-yellow to yellowish-green color, tabular crystal habit, and perfect cleavage in one direction. The most important test, however, is checking for fluorescence – this mineral intensely glows a bright, yellowish-green color under UV light. Confirmation of identity is achieved by measuring radioactivity with a Geiger counter. ## Distinguishing from Similar Minerals Saléeite is very similar to other minerals of the autunite group. The most difficult to distinguish is autunite, which has virtually identical appearance and fluorescence but contains calcium instead of magnesium – differentiation requires chemical analysis. Torbernite, containing copper, is usually green and does not exhibit fluorescence. Nováčekite is a dimorph of saléeite and has very similar properties. Uranophane forms acicular or radial aggregates and usually has a lighter, straw-yellow hue. ## Crystal Forms Saléeite crystallizes in the monoclinic system, but its crystals are pseudotetragonal – they have the form of thin, square or rectangular tablets. These crystals rarely occur individually. They usually form fan-shaped or radial aggregates, rosettes, as well as dense, scaly crusts and coatings on rock surfaces.

Geological environment

## Genesis Saléeite is a secondary mineral, forming in the oxidation (weathering) zones of uranium deposits. It forms as a result of groundwater containing dissolved phosphorus and magnesium acting on primary uranium minerals, such as uraninite. It crystallizes in fissures and voids of sedimentary rocks (mainly sandstones and limestones) and in granites. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals. Its most common associates include torbernite, autunite, uranophane, phosphuranylite, as well as primary uraninite. Iron oxides (goethite, limonite) and quartz are also found in paragenesis. ## Localities Significant deposits and occurrences of saléeite are limited to a few places worldwide. Besides the type locality in Shinkolobwe (DRC), beautiful specimens come from the Ranger mine in the Northern Territory, Australia. It also occurs in the USA, mainly in the states of Utah, Nevada, Arizona, and South Dakota. It is also known from several localities in Europe, including Germany (Saxony) and France (Rhône-Alpes).

Rarity

Uncommon

For collectors

## Quality Criteria The most highly prized saléeite specimens are characterized by sharp, well-formed crystals with high transparency and an intense, lemon-yellow color. Large, single tablets or aesthetically composed fan-shaped aggregates on a contrasting, dark matrix enhance their attractiveness. Specimens rich in crystals, covering a significant surface area of the matrix, are also highly sought after. Value increases when saléeite occurs in association with other rare uranium minerals. ## Popular Localities The Ranger mine in Australia is considered the source of the best quality collector's specimens, yielding large, sharp crystals of magnificent color. Historical specimens from Shinkolobwe in the DRC are also classics, though rarely available on the market. Some finds from uraniferous sandstones in Utah, USA, are also valued.

Care and storage

## Cleaning Saléeite specimens are very delicate and fragile. Only a soft brush or compressed air from a safe distance should be used to remove dust. Contact with water should be avoided; as a hydrated mineral, it can undergo changes, and water can penetrate cleavage planes, weakening the specimen's structure. If wet cleaning is absolutely necessary, use a minimal amount of distilled water and dry the specimen immediately. ## What to Avoid Saléeite is a radioactive mineral. Direct, prolonged skin contact should be avoided, and hands should be washed after each contact. Inhaling dust, which may be produced when crushing or cleaning, is strictly prohibited. The mineral is sensitive to heat and direct sunlight, which can lead to dehydration, causing loss of luster, transparency, and structural changes. It should not be stored in dry and hot conditions. All chemicals and ultrasonics should be avoided. ## Storage Due to radioactivity, saléeite specimens should be stored in closed, sealed containers (e.g., acrylic) that block alpha particles and prevent dust dispersion. The container must be clearly marked with a radioactivity symbol. It is recommended to store it in a location away from permanent human presence, in a well-ventilated room. It should not be kept with minerals sensitive to radiation.

Sources

IMA Mineral List (CNMNC)