Pseudomeisserite-(NH_4_)

Chemical formula: (N₃-H₄)₂Na₄[(U₆+O₂)₂(S₆+O₄)₅]·₄H₂O

Pseudomeisseryite-(NH₄) is a very rare, water-soluble uranyl mineral, found in uranium mines.

## Characteristics Pseudomeisseryite-(NH₄) is a secondary uranium mineral, forming very small, tabular or lath-like crystals, which usually occur in radial or tangled aggregates. Individual crystals rarely exceed 0.2 mm in length. Due to its water solubility, it is an unstable mineral that can only be observed in dry mine conditions. ## Physical Properties Crystals exhibit intense yellowish-green fluorescence under ultraviolet light. The mineral is soft and brittle. It is readily soluble in cold water. ## Colors and Varieties This mineral occurs in colors from pale yellow to greenish-yellow. No varieties have been distinguished. ## History and Name It was approved as a new mineral by the IMA in 2019 (IMA2019-070). Its name refers to its structural similarity to meisseryite, with the prefix "pseudo" indicating a different crystallographic system. The -(NH₄) suffix refers to the dominant ammonium cation in its chemical structure. It was described by Jakub Plášil and his research team. ## Uses Pseudomeisseryite-(NH₄) has no commercial or industrial applications. It is of purely scientific interest and is an object of interest for specialized collectors of uranium minerals.

Properties

Mohs hardness: 2
Luster: Vitreous
Streak: Light yellow
Density: 3.33
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Its key diagnostic feature is its occurrence as fine, yellow or greenish-yellow, radial aggregates in dry parts of uranium mines. Its water solubility and intense yellowish-green fluorescence under UV light are also characteristic. ## Distinguishing from similar minerals It can be confused with other secondary uranyl sulfates, such as meisseryite, johannite, or natrozippeite. Differentiation from meisseryite requires crystallographic analysis (pseudomeisseryite is monoclinic, meisseryite is triclinic). Certain identification is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD) and chemical spectroscopy (EDS). ## Crystal forms It forms very small, thin, tabular crystals with a lath-like habit, elongated along the [010] axis. These crystals combine into radial, stellate, or tangled aggregates.

Geological environment

## Genesis It is a secondary mineral, formed as a result of post-mining processes in uranium mines. It crystallizes from saline mine waters under low humidity conditions, due to the oxidation of uraninite in the presence of pyrite (sulfate source) and organic matter or the decomposition of drilling fluids (ammonium ion source). ## Mineral associations It co-occurs with other secondary uranyl sulfates, such as meisseryite, adrianite, natrozippeite, as well as gypsum and uraninite. ## Localities The only confirmed locality for this mineral (type locality) is the Blue Lizard uranium mine in San Juan County, Utah, USA.

Rarity

Extremely rare

For collectors

## Quality criteria For collectors, the size and richness of aggregates on the rock matrix are most important. Due to the microscopic size of the crystals, specimens are primarily evaluated based on the aesthetics of the entire aggregate and the intensity of its color. Well-formed, radial aggregates are most desirable. ## Popular localities The only known and available specimens for collectors come from the Blue Lizard mine in Utah, USA. This is also its type locality.

Care and storage

## Cleaning The mineral must absolutely not be cleaned wet, as it is readily soluble in water. Any contact with water or even humid air leads to its destruction. Mechanical cleaning is impossible due to the extreme fragility of the specimens. ## What to avoid Avoid water, cleaning solutions, high air humidity, and temperature changes. As a uranium mineral, it is radioactive and should be handled with appropriate precautions, avoiding dust inhalation and direct skin contact. ## Storage Specimens must be stored in sealed, dry containers, preferably with a desiccant (silica gel). They should be kept away from other minerals that could be damaged by its potential decomposition or radioactivity. Store in a location isolated from constant human presence.