Regerite

Chemical formula: KFe₃+₆(PO₄)₄(OH)₇(H₂O)₆·₄H₂O

A very rare, hydrated potassium iron phosphate, forming characteristic, hemispherical aggregates of radial crystals.

## Characteristics Regerite is a secondary mineral that visually manifests as small, hemispherical aggregates with a diameter not exceeding 0.2 mm. These structures are composed of radially divergent, acicular crystals. Typical specimens are yellowish to brownish-yellow and exhibit a vitreous luster. Due to its microscopic size, it is a mineral valued mainly by collectors specializing in microminerals. ## Physical Properties Regerite is a relatively soft mineral, with a Mohs hardness estimated at approximately 2. It is translucent, and its density, calculated based on the chemical formula and unit cell parameters, is 2.43 g/cm³. The luster is described as vitreous. ## Colors and Varieties This mineral occurs in a uniform color range, from yellowish to brownish-yellow. No named color varieties or commercial varieties have been distinguished. ## History and Name Regerite was officially recognized as a new mineral species by the International Mineralogical Association (IMA) in 2021. Its name honors Paul Reger, a German mineral collector who specialized in minerals from the Clara mine and was a co-discoverer of several new species. The type locality (the only known one) is the Clara mine in Wolfach, Black Forest (Germany). ## Applications As an extremely rare mineral occurring only in microscopic specimens, regerite has no industrial application. Its significance is purely scientific and collectible.

Properties

Mohs hardness: 2
Luster: Vitreous
Streak: Pale yellow
Density: 2.43
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification The diagnostic feature of regerite is its unique form of occurrence: small (up to 0.2 mm), hemispherical aggregates with a radial internal structure. Its yellowish-brown color, vitreous luster, and very specific occurrence environment in the Clara mine are also key. ## Distinguishing from Similar Minerals Regerite can be confused with other secondary iron phosphates that form radial aggregates, such as cacoxenite. However, cacoxenite usually has a more golden-yellow color and forms acicular or fibrous aggregates, not necessarily enclosed in such regular hemispheres. Final identification requires advanced analytical methods (e.g., EDS/PXRD), but the characteristic habit combined with the locality is a strong indication. ## Crystal Forms Regerite forms hemispherical aggregates composed of radially arranged, acicular or bladed crystals. Single, isolated crystals are not observed.

Geological environment

## Genesis Regerite is a secondary mineral. It forms in hydrothermal voids of barite veins that cut through gneissic rocks and sandstones. It crystallizes at low temperatures as a result of the alteration of earlier minerals in the presence of phosphorus-rich solutions. ## Mineral Associations This mineral occurs in direct association with goethite, quartz, and minerals from the chlorite group (ferrian-sudoite). Co-occurrence with these minerals is typical for its discovery site. ## Localities The only confirmed locality of regerite in the world is its type locality - the Clara mine (Grube Clara) in the Rankach valley, near Wolfach in the Black Forest, Baden-Württemberg (Germany).

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of regerite specimens, being a micromineral, is assessed based on several criteria. Specimens with well-formed, sharply defined hemispheres of intense, yellowish-brown color are most highly valued. The absence of damage to the delicate aggregates and their number and distribution on the rock matrix are important. A contrasting matrix, e.g., white quartz, enhances the aesthetic value of the specimen.

Care and storage

## Cleaning Regerite specimens are extremely delicate and small. To remove dust, it is best to use a photographic air blower or compressed air from a distance. Any mechanical contact, even with a soft brush, risks destroying the fragile aggregates. Do not use water or any chemicals. ## What to Avoid Ultrasonic cleaners, all chemical solvents, acids, and sudden temperature changes should be absolutely avoided. Its low hardness (approx. 2 on the Mohs scale) makes it susceptible to scratches and mechanical damage. ## Storage Specimens should be stored exclusively in specialized "micromount" boxes that protect them from dust, shocks, and mechanical damage. Store in a dry place, away from direct sunlight.

Sources

IMA Mineral List (CNMNC)