Wildenauerite

Chemical formula: Zn<sup>2+</sup>(Fe<sup>3+</sup><sub>0.5</sub>Mn<sup>2+</sup><sub>0.5</sub>)<sub>2</sub>Mn<sup>2+</sup>Fe<sup>3+</sup>(PO<sub>4</sub>)<sub>3</sub>(OH)<sub>3</sub>(H<sub>2</sub>O)<sub>8</sub>

Wildenauerite is a very rare, hydrated zinc, iron, and manganese phosphate, forming unique, dark green to black, bladed crystals.

## Characteristics Wildenauerite is a complex, hydrated zinc, iron, and manganese phosphate, belonging to the strunzite group. It forms very small, bladed or acicular crystals, which typically do not exceed 1 mm in length. These crystals often occur as radial or tangled aggregates, as well as single needles embedded in quartz. Its color is characteristic, ranging from dark green to almost black. ## Physical Properties Wildenauerite crystals exhibit a vitreous luster. They are brittle, and their Mohs hardness is 3. Due to the small size of the crystals, precise density determination is difficult, but the calculated value is 2.86 g/cm³. The mineral is translucent, especially in smaller fragments. ## Colors and Varieties This mineral occurs in uniform colors, from dark green, through greenish-black, to black. No varieties have been distinguished. ## History and Name Wildenauerite was discovered in the historic Christian iron ore mine in Wildenau, in the Siegerland mountain range in Germany. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2016 (IMA2016-087). Its name comes directly from its type locality - Wildenau. ## Uses Wildenauerite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals and scientists studying phosphate mineralogy.

Properties

Mohs hardness
3
Luster
Vitreous
Streak
Pale green
Density
2.86
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Wildenauerite is identified by its characteristic form - tiny, bladed or acicular crystals forming radial aggregates. Key features also include its dark green to black color, vitreous luster, and co-occurrence with quartz and other phosphates in a specific geological environment. ## Distinguishing from Similar Minerals It can be confused with other dark, acicular minerals from the strunzite group or other phosphates. Final distinction from minerals such as strunzite or laueite requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS), due to subtle differences in composition and structure. ## Crystal Forms Crystals are elongated and flattened (bladed) along the [001] axis and may exhibit striations. They usually form radial, stellate, or haphazardly tangled aggregates. They also occur as single crystals embedded in rock cavities, most often in quartz.

Geological environment

## Genesis Wildenauerite is a secondary mineral that crystallizes under low-temperature hydrothermal alteration conditions. It forms in cavities and fissures within quartz-siderite veins that cut through Devonian sandstones and shales. Its formation is a result of the alteration of earlier minerals in the presence of phosphorus-rich solutions. ## Mineral Associations This mineral occurs in association with quartz, siderite, hematite, goethite, as well as other rare phosphates such as strengite, cacoxenite, beraunite, strunzite, and laueite. ## Localities The only confirmed occurrence of wildenauerite in the world is its type locality - the historic Christian mine in Wildenau, in the Siegerland region, North Rhine-Westphalia, Germany.

Rarity

Very rare

For collectors

## Quality Criteria The most prized wildenauerite specimens are those with well-formed, sharply terminated crystals forming aesthetic, radial aggregates. The contrast with a light quartz background significantly enhances the visual appeal of the specimen. Due to the microscopic nature of the mineral, the size of aggregates and individual crystals is also important, although they rarely exceed a millimeter. ## Popular Localities The only source of specimens is the Christian mine in Wildenau, Germany. Material from this locality is extremely rare and sought after by specialized collectors of systematic minerals and microminerals.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to the brittleness and small size of the crystals, wet cleaning and ultrasonic cleaners should be avoided. ## What to Avoid Avoid contact with all chemicals, acids, and detergents. The crystals are brittle and susceptible to mechanical damage, so they should be protected from impacts and scratches. The specimen should not be heated or exposed to sudden temperature changes. ## Storage Wildenauerite specimens, as microminerals, are best stored in specialized "micromount" boxes, which protect them from dust and mechanical damage. Avoid exposure to direct sunlight, although there is no evidence of fading.

Sources

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