Rauchite

Chemical formula: Ni²⁺(U⁶⁺O₂)₂(As⁵⁺O₄)₂·10H₂O

Rauchite is a rare, secondary uranyl and nickel mineral, forming characteristic, yellowish-green, tabular crystals.

## Characteristics Rauchite is a hydrated uranyl and nickel arsenate, belonging to the meta-autunite group. It occurs as very small, thin, tabular crystals with a square or rectangular outline, usually not exceeding 0.2 mm in size. These crystals often form rosette-like aggregates, fan-shaped clusters, or thin coatings and crusts on rock surfaces. Due to its chemical composition, rauchite is a highly radioactive mineral. ## Physical Properties Rauchite crystals are brittle. The mineral exhibits strong, yellowish-green fluorescence under ultraviolet light, both shortwave and longwave. Its Mohs hardness is approximately 2, and its calculated density is 3.25 g/cm³. ## Colors and Varieties Rauchite has a characteristic, pale yellowish-green color. No color varieties or commercial forms are known. ## History and Name The mineral was discovered in the dumps of the historic "Weißer Hirsch" uranium mine in Schneeberg, Saxony (Germany). It was described and approved by the International Mineralogical Association (IMA) in 2007. The name honors Frank Rauch, a German mineral collector from Schneeberg, who found the first samples of this mineral and brought them to the attention of researchers. ## Applications Due to its extreme rarity and microscopic crystal size, rauchite has no industrial applications. It is solely an object of scientific interest and is valued by specialized collectors of rare uranium minerals.

Properties

Mohs hardness
2
Color
Light yellowish-green, pale green
Luster
Vitreous, Pearly on cleavage planes
Streak
White
Density
3.427
Cleavage
on {001}
Fracture
Micaceous
Transparency
Transparent,Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Characteristic features of rauchite include its pale yellowish-green color, the habit of thin, tabular crystals forming rosette-like aggregates, and strong yellowish-green fluorescence under UV light. Its occurrence in paragenesis with other secondary uranium and nickel minerals is also an important clue. ## Distinguishing from Similar Minerals Rauchite is visually almost identical to other minerals of the meta-autunite group, such as metakahlerite (yellow), metanovacekite (yellow), or meta-autunite (yellowish-green). Definitive differentiation from these minerals is almost exclusively possible using advanced analytical methods, such as chemical analysis (EDS/WDS) or X-ray diffraction (XRD). ## Crystal Forms Rauchite crystallizes in the form of very thin, square or rectangular tablets, oriented on the {001} plane. These crystals combine into fan-shaped, rosette-like, or almost spherical aggregates, and also form thin coatings on the host rock.

Geological environment

## Genesis Rauchite is a secondary mineral, forming in the oxidation (weathering) zones of uranium-nickel-cobalt-arsenic ore deposits. It forms as a result of low-temperature hydrothermal processes, in the presence of solutions rich in uranium, nickel, and arsenic, derived from the weathering of primary minerals such as uraninite and nickel arsenides. ## Mineral Associations This mineral co-occurs with other secondary uranyl arsenates, such as metakahlerite, metanovacekite, meta-autunite, metazeunerite, and uranospinite. It is also accompanied by gypsum, quartz, and iron oxides. ## Localities The only confirmed locality of rauchite in the world (type locality) is the historic mining region of Schneeberg in the Ore Mountains, Saxony, Germany. The mineral was found there in the dumps of the former "Weißer Hirsch" mine.

Rarity

Very rare

For collectors

## Quality Criteria For rauchite collectors, the size and quality of crystal formation, as well as the richness of aggregates on the rock matrix, are most important. Specimens with clearly formed, rosette-like clusters of intense, yellowish-green color, contrasting with the darker host rock, are most valued. Due to the microscopic nature of the mineral, specimens suitable for observation under magnification are most desirable. ## Popular Localities The only source of rauchite specimens is its type locality: Schneeberg in Germany. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Rauchite specimens should generally not be cleaned wet. Due to its fragility and water solubility, cleaning should be limited to very careful dust removal using a soft brush or a photographic air blower. ## What to Avoid Contact with water, acids, and other chemicals that could damage or dissolve the mineral must be strictly avoided. As a secondary mineral, it is unstable under fluctuating humidity conditions. It is highly radioactive – direct skin contact, dust inhalation, and storage in areas of permanent human presence should be avoided. ## Storage Rauchite specimens must be stored in sealed, lead-lined, or appropriately shielded containers with clear radioactivity labeling. It is best to keep them in a dry environment, at a stable temperature, away from sunlight and other minerals that could be damaged by radiation.

External references

Sources

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