Bayleyite
Chemical formula: Mg<sub>2</sub>(U<sup>6+</sup>O<sub>2</sub>)(CO<sub>3</sub>)<sub>3</sub>·18H<sub>2</sub>O
Bayleyite is a rare, secondary uranium mineral, forming bright yellow, water-soluble coatings and acicular crystals in uranium mines.
Properties
- Mohs hardness
- 2-2.5
- Luster
- Vitreous
- Streak
- Yellow
- Density
- 2.05
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Key diagnostic features of bayleyite include its bright, lemon-yellow color, occurrence as delicate, acicular coatings, and strong yellowish-green fluorescence under UV light. Its water solubility is also a characteristic feature. Tests should be performed on a very small sample due to the mineral's rarity. ## Distinguishing from Similar Minerals Bayleyite can be confused with other yellow secondary uranium minerals, such as andersonite, liebigite, tyuyamunite, or carnotite. Andersonite and liebigite are also water-soluble and fluorescent, but they crystallize in different systems (trigonal and orthorhombic) and often form aggregates of small, tabular crystals, rather than acicular ones. Carnotite and tyuyamunite are water-insoluble and usually form earthy or powdery coatings. ## Crystal Forms Bayleyite forms small, prismatic or acicular crystals, often elongated and gathered into radial aggregates, bundles, or tangled, felt-like masses. It also occurs as ephemeral efflorescences and coatings on host rocks or mine walls.
Geological environment
## Genesis Bayleyite is a secondary mineral, formed as a result of weathering and oxidation of primary uranium ores (mainly uraninite). It forms as a post-mining product on the walls and timber supports of old uranium mines, where waters rich in magnesium and carbonates react with uranyl minerals. Its formation is often associated with humid mine environments. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals, such as andersonite, schröckingerite, swartzite, gypsum, uraninite, as well as with dolomite and quartz. ## Localities The most important bayleyite localities worldwide include mines in the Colorado Plateau region in the USA, especially in Utah (e.g., Hideout Mine, Delta Mine), Arizona (Hillside Mine - type locality), and Wyoming. It is also known from Jáchymov in the Czech Republic, Wölsendorf in Germany, and several locations in Australia.
Rarity
Rare
For collectors
## Quality Criteria Specimens most valued by collectors are those with well-formed, sharp, and isolated acicular crystals, forming aesthetic, radial groups on a contrasting rock matrix. The intensity and purity of the lemon-yellow color also significantly increase the specimen's value. Due to its delicacy, undamaged specimens during extraction and transport are rare. ## Popular Localities Classic and most sought-after bayleyite specimens come from mines in San Juan County, Utah, USA. Material from these localities is considered the global standard for this mineral.
Care and storage
## Cleaning Bayleyite is water-soluble, so it must absolutely not be cleaned wet. The only permissible method is very careful dust removal using a soft brush or a photographic air blower. Avoid touching the crystals, which are extremely fragile. ## What to Avoid Avoid contact with water and any liquids that would dissolve it. The mineral is unstable in dry air – it loses hydration water and may disintegrate. It should be protected from high temperatures, direct sunlight, and changes in humidity. Due to its radioactivity, direct contact should be limited, and hands should always be washed after touching it. ## Storage Bayleyite specimens should be stored in tightly sealed containers (e.g., "membrane box" type or vials) which help maintain a stable humidity level and protect delicate crystals from mechanical damage. It should be stored away from other minerals it might damage, and in a place inaccessible to children and pets.