Zellerite
Chemical formula: Ca(U<sup>6+</sup>O<sub>2</sub>)(CO<sub>3</sub>)<sub>2</sub>·5H<sub>2</sub>O
Zellerite is a rare, secondary uranium mineral of intense yellow color, forming acicular crystals and coatings.
Properties
- Mohs hardness
- 2
- Luster
- Silky
- Streak
- Light yellow
- Density
- 2.85
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Characteristic features of zellerite include its intense lemon-yellow color, acicular or fibrous crystal habit forming radial aggregates, and strong fluorescence under ultraviolet light (both shortwave and longwave). It reacts vigorously with hydrochloric acid, releasing carbon dioxide. ## Distinguishing from similar minerals Zellerite can be confused with other yellow secondary uranium minerals, such as meta-zellerite, andersonite, liebigite, or schröckingerite. Meta-zellerite is a dehydration product of zellerite and has very similar properties. Andersonite and liebigite also fluoresce strongly but crystallize in different systems and often form more granular or scaly aggregates. Accurate differentiation of these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal forms Zellerite forms very fine, acicular crystals elongated along the [001] axis. These crystals combine into radial, stellate, or spherulitic aggregates, and also form thin coatings and crusts on rock surfaces.
Geological environment
## Genesis Zellerite is a secondary mineral, formed in the oxidation zones of uranium deposits. It forms as a result of weathering and alteration of primary uranium minerals (such as uraninite) in a carbonate-rich environment. It is a relatively unstable mineral that readily dehydrates in dry air, transforming into meta-zellerite. ## Mineral associations This mineral co-occurs with other secondary uranium minerals, such as meta-zellerite (into which it transforms), schröckingerite, uranophane, gypsum, calcite, as well as native sulfur and iron oxides (limonite). ## Localities The most important and type locality for zellerite is its discovery site – the "Lucky Mc" uranium mine in the Gas Hills area, Fremont County, Wyoming, USA. It is also known from several other locations in the USA, including Utah and Arizona. Outside the United States, its occurrence has been reported in the Svornost mine in Jáchymov, Czech Republic.
Rarity
Very rare
For collectors
## Quality criteria The most prized zellerite specimens are those that exhibit well-formed, radial aggregates of acicular crystals with an intense, lemon-yellow color. Contrast with the rock matrix and the absence of damage to delicate structures are important. Due to its rarity, even small but well-formed micromounts are sought after by specialized collectors. ## Popular localities By far the most classic and sought-after specimens come from the type locality in Gas Hills, Wyoming, USA. Specimens from other localities are extremely rare and are of great value to advanced collectors of uranium minerals.
Care and storage
## Cleaning Zellerite specimens are extremely delicate and fragile. Mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust. Contact with water, which can damage or dissolve the mineral, should be avoided. ## What to avoid Zellerite is sensitive to changes in humidity and temperature. Direct sunlight, which can cause fading and dehydration, should be avoided. It must be protected from all chemicals, acids, and detergents. As a uranium mineral, it is radioactive and requires careful handling – hands should be washed after each contact, and dust inhalation should be avoided. ## Storage Specimens should be stored in closed, stable containers (e.g., "perky box" type) to protect them from mechanical damage, dust, and humidity changes. Store away from frequently occupied areas, in a dry and dark place. It is essential to clearly label it as a radioactive mineral.