Natroboltwoodite
Chemical formula: Na(U⁶⁺O₂)(SiO₃OH)(H₂O)
Natroboltwoodite is a rare, bright yellow uranium mineral, forming acicular crystals and radial aggregates.
Properties
- Mohs hardness
- 4
- Luster
- Vitreous
- Streak
- White
- Density
- 4.1
- Cleavage
- {010} perfect, {001} imperfect.
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Key diagnostic features include its bright yellow color, acicular crystal habit, and the formation of radial aggregates. The mineral exhibits strong, green fluorescence under ultraviolet light (both shortwave and longwave). It is highly radioactive, which can be easily detected with a Geiger counter. ## Distinguishing from Similar Minerals It can be confused with other secondary uranium minerals of similar color and form, such as boltwoodite or uranophane. Boltwoodite is a potassium analog, and differentiation without chemical analysis is impossible. Uranophane often forms more compact, fibrous aggregates, rather than such distinct radial acicular aggregates. ## Crystal Forms It forms elongated, acicular, or hair-like crystals. It is most commonly found in the form of radial, stellate, or spherulitic aggregates, as well as crusts and coatings.
Geological environment
## Genesis Natroboltwoodite is a secondary uranium mineral, forming in the oxidation zones of uranium deposits, mainly in sedimentary rocks such as sandstones. It crystallizes from aqueous solutions rich in uranium, silica, and sodium. ## Mineral Associations It often co-occurs with other secondary uranium minerals, such as uranophane, boltwoodite, as well as with gypsum, calcite, and iron oxides (limonite). ## Localities Important worldwide localities include the Kyzylsai deposit in Kazakhstan (type locality), as well as numerous locations in the USA, especially in Utah, Arizona, and Wyoming. It also occurs in Argentina and Italy.
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens are those with well-formed, sharp acicular crystals forming aesthetic, radial aggregates ("rosettes", "sunbursts") on a contrasting rock matrix. The intensity of color and the size of the aggregates also significantly increase the specimen's value. ## Popular Localities Specimens from deposits in Utah (USA), such as mines in the San Rafael Swell area, are highly valued by collectors for the quality and aesthetics of their crystals.
Care and storage
## Cleaning Specimens should only be dry-cleaned, using compressed air to remove dust. Contact with water is not recommended due to the risk of damaging delicate crystals and possible solubility. ## What to Avoid Absolutely avoid contact with water, acids, and other chemicals. The mineral is brittle and susceptible to mechanical damage. As a uranium mineral, it is radioactive and requires careful handling – hands should be washed after each contact. ## Storage Specimens should be stored in closed, padded containers (e.g., "membrane boxes") to protect against physical damage and limit radiation exposure. They should be kept away from areas of constant human presence, in a dry environment.