Metauranopilite

Chemical formula: (U<sup>6+</sup>O<sub>2</sub>)<sub>6</sub>S<sup>6+</sup>O<sub>4</sub>(OH)<sub>10</sub>·5H<sub>2</sub>O

Metauranopilite is a rare, secondary uranium mineral, forming microscopic, yellow to greenish-yellow acicular crystals, strongly fluorescent under UV light.

## Characteristics Metauranopilite is a mineral belonging to the uranyl sulfate group. It occurs as very fine, acicular or fibrous crystals, which often form crusts, coatings, or spherulitic aggregates. Due to the microscopic size of the crystals, its features are difficult to observe with the naked eye. Typical specimens appear as felt-like or silky masses on the host rock. ## Physical Properties Metauranopilite crystals are extremely delicate and brittle. This mineral exhibits strong, green fluorescence under shortwave and longwave ultraviolet light, which is its key diagnostic feature. It is highly radioactive due to its high uranium content. ## Colors and Varieties Metauranopilite ranges in color from canary yellow, through golden yellow, to greenish-yellow. No commercial or color varieties are distinguished. ## History and Name The mineral's name refers to its chemical and structural relationship with uranopilite. The prefix "meta-" refers to a lower degree of hydration compared to uranopilite. It was described as a distinct mineral species as a result of the redefinition of the uranopilite group, and its status was confirmed by the International Mineralogical Association (IMA). ## Uses Metauranopilite, like other secondary uranium minerals, has no direct industrial application due to its rarity and small accumulations. It is an object of scientific and collecting interest as an indicator of uranium deposit weathering processes.

Properties

Mohs hardness
2.5
Luster
Pearly
Streak
Yellow
Density
4.02
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification The most important diagnostic feature of metauranopilite is its intense green fluorescence under UV light (both shortwave and longwave). Visually, it is characterized by yellow, acicular or fibrous crystals forming felt-like crusts. Strong radioactivity, detectable by a Geiger counter, is another key indicator. ## Distinguishing from Similar Minerals Metauranopilite can be confused with other secondary uranium minerals of similar color and form, such as uranopilite, zippeite, johannite, or uranophane. Uranopilite has a higher degree of hydration and can lose water, transforming into metauranopilite. Accurate differentiation of these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD), although the strong fluorescence of metauranopilite distinguishes it from, for example, uranophane (weak or no fluorescence). ## Crystal Forms It forms very fine, elongated, acicular or bladed crystals, rarely exceeding fractions of a millimeter in length. These crystals aggregate into radial or tangled masses, forming crusts and coatings with a silky or matte appearance.

Geological environment

## Genesis Metauranopilite is a secondary mineral, forming in the oxidation (weathering) zones of uranium deposits. It forms as a result of sulfate-rich waters acting on primary minerals, such as uraninite. It is a product of dehydration of uranopilite under conditions of low air humidity. ## Mineral Associations It co-occurs with other secondary uranium minerals, including uranopilite, gypsum, jarosite, zippeite, uranophane, and johannite. Uraninite often accompanies it as a primary mineral. ## Localities Significant occurrences of this mineral are found in Jáchymov (Czech Republic), Johanngeorgenstadt (Germany), in the Lake Athabasca region (Saskatchewan, Canada), and in many uranium mines in Utah (USA), e.g., the Delta mine.

Rarity

Rare

For collectors

## Quality Criteria For collectors, the most desirable specimens are those with rich, well-formed crusts of intense, bright yellow color. The aesthetics of the entire specimen are important, including the contrast of the mineral's color with the host rock. Due to the microscopic nature of the crystals, their individual form is less important than the overall appearance and coverage of the aggregate surface. Specimens exhibiting strong fluorescence are particularly valued. ## Popular Localities The most classic and prized specimens come from historical localities in Europe, such as Jáchymov in the Czech Republic and the Saxony region in Germany. High-quality specimens also come from mines in the American state of Utah.

Care and storage

## Cleaning This mineral is generally not cleaned. Any attempts at mechanical or chemical cleaning will almost certainly destroy the delicate crystals. Only very careful removal of loose contaminants with a soft brush or a photographic blower, without touching the mineral surface, is permissible. ## What to Avoid Avoid contact with water and any chemicals. The crystals are extremely brittle and sensitive to shock and touch. As a highly radioactive mineral, it requires special precautions. Avoid inhaling dust and direct, prolonged skin contact. Always wash hands after handling the specimen. ## Storage Metauranopilite specimens should be stored in closed, airtight containers (e.g., "perky box" type) to prevent microcrystals from scattering and to protect them from mechanical damage. Due to radioactivity, it should be stored away from areas of permanent human presence, in a marked location, preferably in a radiation-shielding container (e.g., lead) if the collection is larger.

Sources

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