Metauramphite

Chemical formula: (N₃-H₄)₂(U₆+O₂)₂(PO₄)₂·₆H₂O

Metauramphite is a rare, secondary uranyl phosphate mineral, distinguished by its yellow color and radioactivity.

## Characteristics Metauramphite is a mineral belonging to the uranyl phosphate group. It occurs as very small, thin, tabular crystals, which often form rosette-like or radial aggregates, as well as coatings and efflorescences. Its crystals rarely exceed 1 mm in size. Due to its chemical composition, which contains uranium, it is a radioactive mineral. ## Physical Properties Metauramphite crystals exhibit a vitreous to pearly luster, especially on cleavage surfaces. It is a relatively soft mineral. Due to the presence of uranium, its density is high, which is typical for uranyl minerals. ## Colors and Varieties Metauramphite has a characteristic pale yellow to yellowish-green color. No color varieties or commercial varieties are distinguished. ## History and Name The name "metauramphite" refers to its chemical composition (ammonium uranyl phosphate) and its relationship to another mineral, uramphite, with the prefix "meta-" indicating a lower state of hydration. It was described as a new mineral in 1954 based on material from a uranium deposit in the Soviet Union. ## Applications Metauramphite has no industrial application. Its significance is limited to an object of scientific and collecting interest, as a rare and well-defined secondary uranium mineral.

Properties

Mohs hardness: 2.5
Luster: Vitreous, Pearly
Streak: Pale yellow
Density: 3.89
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Tetragonal

Diagnostic features

## Identification Metauramphite can be identified by its characteristic yellow to yellowish-green color, its occurrence as small, tabular crystals forming rosette-like aggregates, and its genesis in the oxidation zones of uranium deposits. A key diagnostic feature is its strong radioactivity, easily detectable with a Geiger counter. Under shortwave ultraviolet radiation, it exhibits strong, green fluorescence. ## Distinguishing from Similar Minerals Metauramphite is visually very similar to many other secondary uranium minerals, especially from the metatorbernite-metaautunite group. It can be confused with metaautunite, metatorbernite, saleeite, or uranocircite. Reliable distinction from these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS), as their physical properties (color, form, hardness) are almost identical. ## Crystal Forms Crystals are very small, thin, in the form of square or rectangular tablets. They typically form radial or rosette-like clusters, as well as fan-shaped aggregates and thin coatings on the host rock.

Geological environment

## Genesis Metauramphite is a rare secondary mineral, formed in the oxidation (weathering) zones of uranium deposits. It forms as a result of the reaction of uranium-rich solutions with phosphates, in the presence of ammonium ions. The source of ammonia can be the decomposition of organic matter (e.g., bat guano in caves) or hydrothermal processes. ## Mineral Associations This mineral co-occurs with other secondary uranium minerals, such as uraninite (as a primary mineral), gypsum, metaautunite, metatorbernite, uranophane, and phosphuranylite. ## Localities The most important and well-documented localities, from which high-quality specimens originate, are: - **United States:** Silver Bell Mine in San Juan County (Utah) and Monument No. 2 Mine in Apache County (Arizona). - **Germany:** Streuberg Mine in Vogtland (Saxony). - **Russia:** Type locality (locus typicus) in an unspecified location in the former USSR.

Rarity

Rare

For collectors

## Quality Criteria The quality of a metauramphite specimen is primarily assessed based on the richness and aesthetics of the crystal aggregates. The most valued specimens are those with well-formed, undamaged crystals forming dense, rosette-like or radial clusters on a contrasting host rock. The intensity and purity of the yellow color also contribute to its attractiveness. Due to the microscopic size of the crystals, specimens are almost exclusively intended for collectors specializing in "microminerals" (micromounts). ## Popular Localities The most sought-after specimens by collectors come from classic localities in the USA, especially from the Silver Bell Mine in Utah, which have provided specimens of exceptional aesthetic quality.

Care and storage

## Cleaning This mineral is very delicate and sensitive to water. Mechanical cleaning is highly inadvisable. If necessary, a stream of compressed air can be used to remove dust. Contact with water should be avoided, as it can cause dissolution or transformation into other mineral phases. ## What to Avoid - **Water and moisture:** Metauramphite is unstable in contact with water. It should be stored in very low humidity conditions. - **High temperature:** Heating leads to further dehydration and decomposition of the mineral. - **Sunlight:** Prolonged exposure to sunlight is not recommended, although moisture and temperature remain the main threats. - **Chemicals:** It is easily soluble in acids. - **Vibrations and impacts:** Crystals are brittle and extremely delicate. ## Storage Metauramphite specimens must be stored in sealed, transparent containers (so-called "micromount boxes"), preferably with a desiccant (e.g., silica gel). Due to its radioactivity, it should be stored away from other radiation-sensitive minerals, in a location distant from permanent human presence and appropriately marked.

Sources

IMA Mineral List (CNMNC)