Kahlerite

Chemical formula: Fe²⁺(U⁶⁺O₂)₂(As⁵⁺O₄)₂(H₂O)₆·₆H₂O

Kahlerite is a rare, radioactive mineral from the autunite group, forming characteristic, tabular crystals of an intensely yellow color.

## Characteristics Kahlerite is a hydrated uranyl iron arsenate belonging to the autunite group. This mineral forms thin, square or octagonal crystals with a tabular habit, often with truncated corners. It occurs as individual crystals, rosette-like aggregates, or thin coatings and crusts on the host rock. Due to its uranium content, it is a highly radioactive mineral and exhibits intense, greenish-yellow fluorescence under ultraviolet light (both short-wave and long-wave). ## Physical Properties Kahlerite is a very soft mineral, with a Mohs hardness of 2-2.5. The crystals are brittle and exhibit perfect cleavage in one direction, parallel to the base of the tablets, which causes them to easily separate into thinner lamellae. The luster is vitreous, and on cleavage surfaces, it can be pearly. It is transparent. ## Colors and Varieties This mineral has a characteristic sulfur-yellow or lemon-yellow color. No color or commercial varieties are distinguished. ## History and Name Kahlerite was first described in 1953. Its name commemorates the Austrian geologist Franz Kahler (1900-1995) and his wife, Gusti Kahler, in recognition of their contribution to geological research in Carinthia. The type locality, from which the first described specimens originated, is Hüttenberger Erzberg in Carinthia, Austria. ## Uses Due to its rarity and small accumulations, kahlerite has no industrial application. It is of purely scientific and collector's interest, being a sought-after uranyl mineral.

Properties

Mohs hardness: 2-2.5
Luster: Vitreous, Pearly
Streak: Yellow
Density: 0
Cleavage: {001}
Fracture: Uneven
Transparency: Transparent
Crystal system: Tetragonal

Diagnostic features

## Identification Kahlerite is most easily recognized by its characteristic, thin, square, sulfur-yellow crystals. A key diagnostic feature is its very strong, greenish-yellow fluorescence under UV light. Its occurrence in the oxidation zones of uranium deposits is also an important clue. It is a highly radioactive mineral, which can be confirmed with a Geiger counter. ## Distinguishing from Similar Minerals Kahlerite can be confused with other minerals from the autunite group, such as autunite, torbernite, or zeunerite. - **Autunite** (with calcium) usually has a more greenish hue and slightly different fluorescence. - **Torbernite** (with copper) is green and does not fluoresce. - **Zeunerite** (with copper) is green and has weaker fluorescence. Final differentiation from other yellow uranyl arsenates (like nováčekite) often requires advanced chemical analysis (EDS). ## Crystal Forms Crystals are thin-tabular, with a square or octagonal habit, often with truncated corners. They occur as individual lamellae, in fan-shaped or rosette-like aggregates, as well as thin coatings and crusts.

Geological environment

## Genesis Kahlerite is a secondary uranium mineral, formed in the oxidation (weathering) zones of hydrothermal ore deposits containing uraninite and arsenic minerals (e.g., arsenopyrite). It forms as a result of arsenic-rich waters acting on primary uranium minerals in the presence of iron. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals, such as metakahlerite (its partially dehydrated form), zeunerite, uraninite, as well as with quartz, hematite, and various sulfides. ## Localities The most important and classic occurrences of kahlerite are in Austria, at the type locality of Hüttenberger Erzberg in Carinthia. It is also known from several other locations worldwide, including uranium mines in the Schneeberg region in Saxony (Germany) and some pegmatites in the USA.

Rarity

Rare

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, sharp crystals of intense, lemon-yellow color. Groups of crystals forming aesthetic rosettes or fans on a contrasting rock matrix are highly prized. Crystal size is also important, although even well-formed microcrystals are sought after. Due to the mineral's brittleness, specimens without mechanical damage are significantly more valuable. ## Popular Localities Classic and most desirable specimens come from the type locality in Hüttenberg, Austria. Specimens from German localities, such as Schneeberg, are also valued in specialized collections.

Care and storage

## Cleaning Kahlerite specimens are extremely delicate and brittle. Cleaning should be limited to an absolute minimum. If necessary, a very soft brush can be used to remove loose dust particles. Avoid contact with water, which can damage the mineral. ## What to Avoid - **Water and Chemicals:** Contact with water, acids, or other cleaning agents is prohibited. The mineral is soluble and can be destroyed. - **Shocks and Ultrasound:** Ultrasonic cleaners and any impacts or vibrations will cause the brittle crystals to disintegrate. - **High Temperature and Light:** Avoid direct sunlight and high temperatures, which can lead to dehydration (loss of water from the crystal lattice) and destruction of the mineral's structure. - **Radioactivity:** As a uranium mineral, kahlerite is radioactive. Hands should be washed after each contact with the specimen, and it should not be stored in places of permanent human presence (desk, bedroom). ## Storage Specimens should be stored under stable conditions, in closed, padded "micromount" boxes to protect them from mechanical damage, dust, and humidity changes. Due to radioactivity, it is recommended to store them in special containers (e.g., lead-lined) or in a designated area of the collection, away from other radiation-sensitive minerals.

External references

https://www.mindat.org/min-2131.html