Zdenĕkite

Chemical formula: NaPb<sup>2+</sup>Cu<sup>2+</sup><sub>5</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>4</sub>Cl·5H<sub>2</sub>O

Zdeněkite is a very rare, secondary copper and lead mineral with an intensely blue-green color, forming small, platy crystals.

## Characteristics Zdeněkite is a hydrated sodium, lead, and copper arsenate with an additional chloride anion. It occurs as very small, thin, platy crystals, often with a hexagonal outline, rarely exceeding 0.5 mm. These crystals form rosette-like or radial aggregates, as well as thin crusts and coatings on the host rock. Its most characteristic feature is its vivid, blue-green color. ## Physical Properties This mineral is characterized by a vitreous luster. It is transparent to translucent. Due to the small size of the crystals, hardness and density have not been precisely measured, but the density calculated based on the formula and cell parameters is 4.11 g/cm³. ## Colors and Varieties Zdeněkite occurs in a uniform, characteristic blue-green color. No color varieties or commercial varieties are known. ## History and Name The mineral was discovered on the historical dump of the "Sophia" mine in Wittichen, German Black Forest. It was approved by the IMA in 1992. The name honors the Czech mineralogist and crystallographer, Professor František Zdeněk (1931-1991) from Charles University in Prague, in recognition of his contribution to mineralogy. ## Uses Zdeněkite has no industrial application. It is of purely scientific and collectible interest as a very rare secondary mineral.

Properties

Luster
Vitreous
Streak
Light green
Density
4.11
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features include its characteristic blue-green color, occurrence as small, platy crystals forming rosette-like aggregates, and paragenesis with other secondary copper and lead arsenates. Final identification requires advanced analytical methods (e.g., XRD, EDS). ## Distinguishing from Similar Minerals Zdeněkite can be confused with other secondary copper minerals of similar color, such as agardite, mixite, or cyanotrichite. However, it is distinguished by its specific platy crystal habit and hexagonal outline. Mixite and agardite typically form acicular or fibrous aggregates, while cyanotrichite occurs as felted masses. ## Crystal Forms It forms thin, platy crystals with a hexagonal or pseudohexagonal outline. These crystals combine into radial or rosette-like aggregates, and also form thin crusts on rock surfaces.

Geological environment

## Genesis Zdeněkite is a secondary mineral, formed in the oxidation zones of polymetallic ores rich in copper, lead, and arsenic. It forms as a result of the weathering of primary ore minerals in the presence of chloride-containing solutions. ## Mineral Associations It most often co-occurs with other rare secondary minerals, such as agardite, olivenite, cornwallite, mimetite, bayldonite, duftite, as well as with quartz, baryte, and goethite. ## Localities The most important and type locality is the "Sophia" mine in Wittichen, Black Forest, Germany. Its occurrence has also been confirmed in the historical mining district of Jáchymov in the Czech Republic and in the "Maria Josefa" mine in Rodalquilar, Spain. All these localities provide only microscopic specimens.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of zdeněkite depends on the richness and aesthetics of the crystal aggregates on the rock matrix. Specimens with clearly formed, undamaged rosettes of platy crystals of intense, blue-green color, contrasting well with the substrate, are most valued. Due to the microscopic size of the crystals, the quality of the specimen when viewed under magnification is crucial. ## Popular Localities The only source of specimens available on the collector's market is the historical type locality - the "Sophia" mine in Wittichen, Germany. Specimens from other confirmed localities are extremely rare and practically unavailable commercially.

Care and storage

## Cleaning Specimens should only be cleaned very carefully, using compressed air to remove dust. Due to its extreme delicacy and solubility, contact with water and all cleaning fluids should be avoided. ## What to Avoid Water, chemicals (especially acids), ultrasound, and high temperatures must be strictly avoided. The mineral is sensitive to changes in humidity and can be damaged by careless handling. ## Storage It is recommended to store specimens in sealed, lockable "micromount" boxes to protect them from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight and sudden temperature changes.

Sources

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