Nollmotzite

Chemical formula: Mg[U<sup>5+</sup>(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>O<sub>4</sub>F<sub>3</sub>]·4H<sub>2</sub>O

Nollmotzite is an extremely rare uranyl mineral, distinguished by its unique chemical composition containing magnesium and fluorine.

## Characteristics Nollmotzite is a secondary uranyl mineral, occurring as very small, bladed or acicular crystals that form radial aggregates or rosettes. Crystals rarely exceed 0.2 mm in length. Due to its chemical composition, which includes uranium, this mineral is radioactive. ## Physical Properties Crystals exhibit strong pleochroism – changing color depending on the viewing direction, from almost colorless to pale yellow. The luster is vitreous. Due to the small size of the crystals, many physical properties, such as hardness and density, have not been precisely determined. ## Colors and Varieties This mineral occurs in yellow to greenish-yellow. No varieties have been identified. ## History and Name Nollmotzite was described as a new mineral in 2023 by Travis A. Olds and co-authors. The name comes from the discovery locality – the dump of a former uranium mine near the village of Nollmotz, in the municipality of Strengberg in Lower Austria. This is the only known occurrence of this mineral in the world (type locality). ## Uses Nollmotzite has no industrial application. Due to its extreme rarity, microscopic size, and recent discovery, it is of purely scientific interest and is an object of interest for specialized collectors of rare minerals.

Properties

Luster
Vitreous
Streak
Pale yellow
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Practical identification of nollmotzite is impossible without advanced analytical methods, such as Raman spectroscopy or chemical analysis using an electron microprobe (EDS). Preliminary indications may include its yellow color, crystal habit, and co-occurrence with other secondary uranium minerals at the known locality. ## Distinguishing from Similar Minerals It can be confused with many other yellow secondary uranyl minerals, such as schoepite, metaschoepite, or compreignacite, which can form similar aggregates. Definitive differentiation requires specialized laboratory equipment. ## Crystal Forms It forms very small, bladed or acicular crystals, typically grouped into radial aggregates, rosettes, or chaotic clusters on the host rock.

Geological environment

## Genesis Nollmotzite is a secondary mineral that forms in the oxidation zone (weathering) of uranium deposits. It forms as a result of groundwater interaction with primary uranium minerals, such as uraninite, in the presence of magnesium and fluorine originating from the surrounding rocks. ## Mineral Associations At the type locality, it co-occurs with other uranyl minerals such as schoepite, compreignacite, rutherfordine, as well as quartz, fluorite, and calcite. ## Localities The only confirmed locality in the world is the dump of a former, small uranium mine near Nollmotz, Strengberg, Lower Austria, Austria.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its extreme rarity and microscopic nature, every specimen is valuable to specialized collectors. The most highly prized specimens are those with clearly formed, rich crystal aggregates, well visible under a microscope, on a contrasting rock matrix. The size of the aggregates and the aesthetic arrangement on the host rock are key factors. ## Popular Localities The only source of specimens is the type locality in Austria. Material from this location is extremely difficult to obtain.

Care and storage

## Cleaning Specimens should be handled with the utmost care. Cleaning is not recommended due to the extreme fragility and small size of the crystals. If absolutely necessary, compressed air can be used from a safe distance to remove dust. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and any mechanical stress. As a uranium mineral, it is radioactive – limit exposure and avoid inhaling dust. Always wash hands after handling the specimen. ## Storage Store in a stable, dry environment, in a sealed container (e.g., a "micromount" box) with appropriate radioactivity labeling. Keep it away from other minerals that may be sensitive to radiation (e.g., smoky quartz, some fluorites).

Sources

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