Tyuyamunite

Chemical formula: Ca(U⁶⁺O₂)₂(V⁵⁺O₄)₂·₅-₈H₂O

Tyuyamunite is a bright yellow, secondary uranium and vanadium mineral, forming characteristic scaly coatings and aggregates.

## Characteristics Tyuyamunite is a mineral from the carnotite group, belonging to the class of hydrated uranyl vanadates. It most often occurs as earthy or scaly aggregates, coatings, and crusts on host rocks. Less frequently, it forms small, tabular crystals with a rhombic outline, often grouped into fan-shaped or rosette aggregates. Its most characteristic feature is its intense, canary-yellow or lemon-yellow color. ## Physical Properties This mineral is very soft, with a Mohs hardness of 1.5-2, meaning it can be scratched with a fingernail. The crystals exhibit perfect, mica-like cleavage in one plane, causing aggregates to easily separate into small flakes. It is a light mineral, with a density of approximately 3.57 g/cm³. It does not exhibit fluorescence under ultraviolet radiation, which distinguishes it from many other secondary uranium minerals. ## Colors and Varieties The dominant color of tyuyamunite is a bright, canary or lemon yellow. Under prolonged exposure to sunlight, its color may change to greenish-yellow. In transmitted light, it is colorless to pale yellow. There are no commercial or colored varieties distinguished. ## History and Name The mineral's name comes from its first discovery and description site – the Tyuya-Muyun deposit in Kyrgyzstan. It was formally described as a new mineral species in 1912. The name directly refers to this historical location. ## Uses Due to its uranium and vanadium content, tyuyamunite, in areas of high concentration, was locally used as a minor ore of these metals. Currently, it is primarily of scientific and collector's interest as an indicator of uranium mineralization.

Properties

Mohs hardness: 1.5-2
Luster: Pearly,Waxy,Dull
Streak: Yellowish
Density: 3.57
Cleavage: Perfect on {001}, micaceous; distinct on {100} & {010}.
Fracture: Micaceous
Transparency: Translucent,Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Tyuyamunite is relatively easy to identify based on its characteristic, bright, canary-yellow color, very low hardness, and typical occurrence as scaly or earthy coatings. Its excellent, mica-like cleavage is also a key feature. ## Distinguishing from Similar Minerals - **Carnotite:** It is visually very similar and often co-occurs with tyuyamunite. Carnotite contains potassium instead of calcium. Differentiation without chemical analysis is practically impossible. Sometimes it is suggested that carnotite has a slightly greener hue, but this is not a rule. - **Autunite:** Exhibits very strong, green fluorescence under UV light, which tyuyamunite does not possess. - **Native sulfur:** Has a similar color, but is harder, lighter, and occurs in completely different geological environments (most often volcanic). ## Crystal Forms This mineral forms very small, thin, tabular crystals with a rhombic outline. These crystals rarely occur individually, most often forming fan-shaped, rosette, or radial aggregates. However, the most common form of occurrence is microcrystalline, scaly, or earthy aggregates forming crusts and coatings.

Geological environment

## Genesis Tyuyamunite is a secondary mineral, formed in the oxidation zone of uranium and vanadium deposits. It forms as a result of the weathering of primary uranium minerals (mainly uraninite) in the presence of solutions rich in vanadium and calcium. It most often occurs in sedimentary rocks, such as sandstones, limestones, or mudstones, where it precipitates in fissures, rock pores, or as impregnations. ## Mineral Associations This mineral often co-occurs with other secondary uranium and vanadium minerals. Its most common associations include carnotite, metatyuyamunite, uranophane, gypsum, calcite, and iron and manganese oxides. ## Localities The most important and historical occurrence, which is the type locality, is the Tyuya-Muyun deposit in Kyrgyzstan. Significant deposits and beautiful specimens also come from the Colorado Plateau region in the USA (states of Utah, Colorado, Arizona, New Mexico), where it was an important component of uranium ores. Other known localities include South Dakota in the USA and some deposits in Kazakhstan.

Rarity

Not very common

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, even microscopic, crystals forming fan-shaped or rosette aggregates. An intense, pure, canary-yellow color is a key factor influencing attractiveness. Rich crusts covering a significant surface of the host rock, creating an aesthetic contrast, are also highly valued. The purity of the specimen, i.e., the absence of impurities and mechanical damage, is also very important. ## Popular Localities Specimens from classic localities on the Colorado Plateau in the USA, such as mines in San Juan County (Utah) or Montrose County (Colorado), are considered standard and are highly regarded. Material from the historical type locality in Kyrgyzstan, although less frequently available, also holds great value for specialized collectors.

Care and storage

## Cleaning Tyuyamunite specimens are extremely delicate and fragile. Cleaning should be kept to an absolute minimum. Only gentle brushing with a soft brush to remove dust is permissible. Avoid any contact with water and other liquids. ## What to Avoid - **Water and moisture:** The mineral is soluble in water and acids. Contact with moisture leads to its damage and loss of cohesion. - **Shocks and friction:** Due to its low hardness and perfect cleavage, it is very susceptible to mechanical damage, scratches, and crumbling. - **Sunlight:** Prolonged exposure to sunlight can cause a color change to a greenish hue. - **Direct contact:** As a uranium mineral, it is radioactive. Avoid direct skin contact, do not inhale dust, and always wash hands after handling a specimen. ## Storage Tyuyamunite specimens should be stored in dry, stable conditions, preferably in sealed, transparent containers (e.g., "micromount" type), which protect them from dust, moisture, and mechanical damage. Due to radioactivity, it should not be stored in bedrooms or areas of constant occupancy. It should be kept away from children and pets.