Ammoniomathesiusite
Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)<sub>5</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>4</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>4</sub>(V<sup>5+</sup>O<sub>5</sub>)·4H<sub>2</sub>O
Ammoniomathesiusite is a very rare, secondary uranyl mineral, distinguished by its intense yellow color and occurrence as coatings and aggregates.
Properties
- Luster
- Vitreous to pearly
- Streak
- Light yellow
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Key diagnostic features include its bright yellow color, occurrence as fine-grained coatings and microscopic, bladed crystals in paragenesis with other secondary uranium minerals. Its genesis, associated with the weathering of uraninite, is also characteristic. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or spectroscopy. ## Distinguishing from similar minerals Ammoniomathesiusite can be confused with many other yellow-colored secondary uranyl minerals, such as mathesiusite, zippeite, johannite, or uranophane. Mathesiusite contains potassium instead of the ammonium group, which is impossible to distinguish visually. The differences between these minerals are subtle and most often concern the form of microcrystals and paragenesis, but certain differentiation is only possible through chemical analysis. ## Crystal forms It forms very small, bladed or acicular crystals, elongated along the [010] axis and flattened parallel to {001}. These crystals group into spherical or hemispherical aggregates, rosettes, and thin crusts and coatings on the host rock.
Geological environment
## Genesis Ammoniomathesiusite is a secondary mineral, forming in the oxidation (weathering) zone of uranium deposits. It forms as a result of the action of sulfate- and ammonia-rich solutions on uraninite. The ammonia in this process likely originates from the decomposition of organic matter (e.g., coal) present in the host rock (sandstone). ## Mineral associations It co-occurs with other secondary uranium minerals, such as gypsum, ammoniozippeite, natrozippeite, johannite, uranophane, as well as with uraninite (as a primary mineral) and pyrite. ## Localities The only confirmed and described occurrence of this mineral in the world is its type locality - the Blue Lizard mine, Red Canyon, San Juan County, Utah, USA.
Rarity
Extremely rare
For collectors
## Quality criteria For collectors, the intensity and purity of the yellow color of the coatings and the richness of the coverage on the rock matrix are most important. Specimens on which well-formed, albeit microscopic, crystalline aggregates are visible (under magnification) are more highly valued. Contrast with the dark host rock also enhances the visual appeal of the specimen. ## Popular localities All known collectible specimens come from a single location in the world: the Blue Lizard mine in Utah, USA. This makes the mineral extremely desirable for specialized collectors of rare and uranium minerals.
Care and storage
## Cleaning Specimens should not be wet cleaned. Dust can only be removed with a soft brush or compressed air from a safe distance. Extreme caution should be exercised due to the fragility and delicacy of the coatings. ## What to avoid Contact with water and any chemicals that could dissolve or damage the mineral should be strictly avoided. As a secondary mineral, it is unstable in a humid environment. It is sensitive to heat. Due to its uranium content, exposure should be limited, and hands should always be washed after contact with the specimen. ## Storage Specimens should be stored in a dry place, preferably in a sealed, closable "perky box" to protect them from moisture, dust, and mechanical damage. Store away from minerals that may be sensitive to radiation.