Richelsdorfite

Chemical formula: Ca₂Cu²⁺₅Sb⁵⁺(As⁵⁺O₄)₄(OH)₆Cl·6H₂O

Richelsdorfite is a very rare, turquoise-blue copper calcium antimony arsenate, forming microscopic, bladed crystals.

## Characteristics Richelsdorfite is a complex, hydrated copper calcium antimony arsenate chloride. It occurs as very small, bladed or acicular crystals, which rarely exceed fractions of a millimeter in length. These crystals often form radial aggregates, rosettes, or coatings on the surface of the host rock. Due to its size, it is a typical micromount mineral, requiring magnification for observation. ## Physical Properties This mineral is characterized by low hardness, 2 on the Mohs scale, which means it is very soft and susceptible to scratching. It has a vitreous luster. It is a translucent mineral. ## Colors and Varieties Richelsdorfite occurs in a characteristic, intense turquoise-blue color. No color or commercial varieties are known. ## History and Name The mineral's name comes from its discovery locality - the Richelsdorf Mountains (Richelsdorfer Gebirge) in Hesse, Germany. It was first described in 1982 by K. Schmetzer, W. Horn, and H. Bank, and its type locality is the Wilhelm mine near Nentershausen. ## Uses Richelsdorfite has no industrial application. Its significance is purely scientific and as a collector's item, being a very rare and aesthetic micromount mineral.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
White
Density
0
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Richelsdorfite can be identified by its characteristic turquoise-blue color, radial aggregates composed of fine, bladed crystals, and its occurrence in the oxidation zones of copper ore deposits. However, definitive identification requires advanced analytical methods, such as chemical analysis (EDS) or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other secondary copper minerals of similar color, such as turquoise, chrysocolla, tyrolite, or aurichalcite. It differs from turquoise and chrysocolla by its crystal habit (blades, needles). From tyrolite and aurichalcite, which also form similar aggregates, it can be distinguished based on chemical analysis (presence of antimony and calcium) and detailed crystallographic studies. ## Crystal Forms It forms elongated, bladed crystals with a rhombic cross-section, often flattened. These crystals combine into characteristic radial or stellate aggregates, and also form thin crusts and coatings.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zones (so-called gossans) of copper ore deposits, particularly those containing barium, arsenic, and antimony minerals. It forms as a result of the weathering of primary sulfides in the presence of oxygen-rich waters. ## Mineral Associations It most often co-occurs with minerals such as barite, quartz, tennantite, chalcopyrite, as well as other secondary copper and arsenic minerals. ## Localities The most important and type locality is the Wilhelm mine in Nentershausen, Hesse, Germany. This is the only confirmed and well-documented locality for this mineral worldwide.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued specimens are those that possess well-formed, distinct crystals forming aesthetic, radial aggregates on a contrasting matrix (e.g., on white barite). The intensity and purity of the turquoise-blue color also significantly increase the specimen's value. Due to the microscopic size of the crystals, the quality of their formation and the richness of the aggregate are crucial. ## Popular Localities The only source of collector specimens is the type locality - the Wilhelm mine in Hesse (Germany). All specimens available on the market originate from this single location.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using compressed air to remove dust. Any contact with water or chemicals is highly inadvisable due to the mineral's solubility and delicacy. ## What to Avoid Avoid contact with water, acids, detergents, and all chemical agents. The mineral is very soft and brittle, so it should be protected from shocks, impacts, and abrasion. It should not be heated or exposed to prolonged sunlight. ## Storage Richelsdorfite specimens, as typical micromounts, should be stored exclusively in specialized, sealed perky boxes, which protect them from dust, moisture, and mechanical damage.

External references

Sources

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