Désorite

Chemical formula: Pb<sup>2+</sup><sub>2</sub>(Fe<sup>3+</sup><sub>6</sub>Zn<sup>2+</sup>)O<sub>2</sub>(PO<sub>4</sub>)<sub>4</sub>(OH)<sub>8</sub>

Désorite is a very rare, dark brown to black phosphate mineral of the beraunite group, found in only one locality worldwide.

## Characteristics Désorite is a very rare phosphate mineral belonging to the beraunite group. It forms very small, lath-like or tabular crystals, which typically occur as radial or tangled aggregates. Individual crystals rarely exceed 0.2 mm in length. The mineral is dark brown to black and opaque. ## Physical Properties Désorite crystals exhibit a vitreous to slightly metallic luster. The Mohs hardness has not been precisely determined but is estimated to be around 3. The mineral is brittle, and its density, calculated from the chemical formula and unit cell parameters, is 4.45 g/cm³. ## History and Name The mineral was approved by the International Mineralogical Association (IMA) in 2022. Its name honors Édouard Désor (1811–1882), a Swiss geologist and paleontologist who made significant contributions to the study of the geology of the Alps and Jura, as well as to glaciology and prehistoric archaeology.

Properties

Mohs hardness
3
Luster
Vitreous to Sub-Metallic
Streak
Brown
Density
4.45
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of désorite is practically only possible using advanced analytical methods, such as Raman spectroscopy and chemical analysis (EDS/WDS). Visually, it is indistinguishable from many other dark secondary minerals, especially those from the beraunite group. ## Distinguishing from Similar Minerals It can be confused with other minerals from the beraunite group (beraunite, eleonorite), as well as with cacoxenite or strengite. Definitive differentiation requires specialized laboratory equipment. ## Crystal Forms It forms small, lath-like crystals, elongated along the [010] axis and flattened parallel to {100}. These crystals combine to form radial or chaotically arranged aggregates.

Geological environment

## Genesis Désorite is a secondary mineral that formed as a result of hydrothermal processes or weathering in the oxidation zone of polymetallic deposits. It occurs in vugs and small rock cavities. ## Mineral Associations At its type locality, it coexists with quartz, strengite, dufrénite, cacoxenite, rockbridgeite, and tinticite. ## Localities The only confirmed occurrence worldwide is the historical Rothläufchen iron mine in Waldgirmes, near Wetzlar in Hesse, Germany. This is the type locality for this mineral.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" mineral of scientific value, the most important criterion is the certainty of specimen identification. The richness and quality of crystals in the microscope's field of view, as well as aesthetic associations with other minerals, are important. The size of aggregates and their degree of development also increase the specimen's value. ## Popular Localities The only source of specimens is the type locality – the Rothläufchen mine in Germany. Material from this location is highly prized by collectors specializing in rare and systematic minerals.

Care and storage

## Cleaning Due to its extreme rarity and fragility, specimens should not be cleaned mechanically or chemically. If necessary, compressed air (from a safe distance) can be used to remove dust. ## What to Avoid Avoid contact with all chemicals, acids, and ultrasonic cleaners. The mineral is brittle and susceptible to mechanical damage. ## Storage Désorite specimens should be stored exclusively in specialized "micromount" boxes, protecting them from physical damage, dust, and sudden changes in environmental conditions.

Sources

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