Wilhelmvierlingite

Chemical formula: CaMn<sup>2+</sup>Fe<sup>3+</sup>(PO<sub>4</sub>)<sub>2</sub>(OH)·2H<sub>2</sub>O

Wilhelmvierlingite is a rare phosphate mineral with a characteristic reddish-brown color, found in granitic pegmatites.

## Characteristics Wilhelmvierlingite is a hydrated phosphate of calcium, manganese, and iron. It forms very small, bladed or thin, tabular crystals, rarely exceeding 1 mm in length. They typically occur as radial or spherulitic aggregates, as well as single, scattered flakes on the surface of other minerals. Due to the small size of the crystals, its visual features are difficult to observe without magnification. ## Physical Properties The crystals exhibit a vitreous luster. The Mohs hardness is approximately 4. The mineral is brittle, and its calculated density is 3.11 g/cm³. It is transparent to translucent. ## Colors and Varieties Wilhelmvierlingite has a characteristic reddish-brown color. No varieties have been distinguished. ## History and Name The mineral was discovered at the Hagendorf-Süd farm in Bavaria (Germany) and described in 1983 by A. Mücke. The name honors Wilhelm Vierling (1905-1974), a German mineral collector from Hagendorf, who first found this mineral and brought it to the attention of researchers. ## Uses Wilhelmvierlingite has no industrial application. It is of purely scientific and collector's interest as a rare mineralogical species.

Properties

Mohs hardness
4
Luster
Vitreous
Streak
Light brown
Density
3.11
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of wilhelmvierlingite is primarily based on its characteristic appearance under magnification – it forms reddish-brown, radial aggregates composed of tiny, bladed crystals. The locality (granitic pegmatites) and co-occurrence with other rare phosphates are also key. ## Differentiation from Similar Minerals It can be confused with other microcrystalline, secondary phosphates of similar color, such as strengite or cacoxenite. Definitive differentiation requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS), due to the small crystal size and visual similarity to other minerals in this group. ## Crystal Forms Crystals are very small, thin-tabular or bladed, elongated along one axis. They most often form radial, stellate, or spherulitic aggregates, as well as rosettes.

Geological environment

## Genesis Wilhelmvierlingite is a secondary phosphate mineral that forms in the oxidation zones of granitic pegmatites. It forms as a result of hydrothermal alteration of primary phosphates, such as zwieselite, in the presence of calcium-rich solutions. ## Mineral Associations This mineral co-occurs with other phosphates, such as strengite, stewartite, laueite, pseudolaueite, rockbridgeite, jahnsite-(CaMnFe), mitridatite, as well as with quartz, muscovite, and iron oxides (limonite). ## Localities The most important and type locality is the Hagendorf-Süd quarry in Waidhaus, Upper Palatinate, Bavaria (Germany). This is the only confirmed and well-documented locality for this mineral worldwide.

Rarity

Very rare

For collectors

## Quality Criteria As a mineral occurring exclusively in the form of microscopic crystals, its collector's value depends on the quality of these crystals. Specimens with well-formed, sharp, and undamaged radial aggregates are most prized. Contrast with the matrix and the presence of rare associated minerals are also important. The size of the aggregates, although usually not exceeding 1-2 mm, also affects the attractiveness of the specimen. ## Popular Localities The only source of collector specimens is the historical type locality – Hagendorf-Süd in Germany. Specimens from this location are highly sought after by collectors specializing in mineral systematics and microminerals.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to their fragility and small crystal size, mechanical cleaning, including brushes, should be avoided. The use of water is not recommended due to the risk of damaging delicate aggregates and potential reactions with associated minerals. ## What to Avoid Avoid contact with all chemicals, including acids and detergents. The mineral is brittle and sensitive to shocks and ultrasound. It should be protected from high temperatures and humidity. ## Storage Wilhelmvierlingite specimens, as microminerals, are best stored in specialized "micromount" boxes, which protect them from dust, mechanical damage, and sudden changes in humidity.

Sources

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