Erikapohlite

Chemical formula: (&#9744;<sub>0.5</sub>Cu<sup>2+</sup><sub>0.5</sub>)Cu<sup>2+</sup>CaZn<sup>2+</sup><sub>2</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>3</sub>·H<sub>2</sub>O

Erikapohlite is a very rare copper, calcium, and zinc arsenate, forming unique, blue-green bladed crystals.

## Characteristics Erikapohlite is a complex arsenate containing copper, calcium, and zinc. This mineral forms very small, bladed or thin, tabular crystals, rarely exceeding 0.2 mm in length. These crystals occur as radial aggregates or rosettes, as well as single, scattered flakes on the surface of the host rock. Its characteristic feature is an intense, blue-green color. ## Physical Properties Erikapohlite crystals exhibit a vitreous luster. Due to the small size of the crystals, many physical properties, such as hardness or density, have not been precisely determined. The density calculated based on the chemical formula and unit cell parameters is 4.31 g/cm³. ## Colors and Varieties This mineral occurs in a uniform, blue-green color. No color varieties or commercial varieties are known. ## History and Name Erikapohlite was discovered on the historic dump of the Maria-Josefa mine in Essershausen, Hesse (Germany). It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2015 (IMA2015-064). The name honors Erika Pohl (born 1940), a German mineral collector who, together with her husband Dagmar Pohl, collected and made available for research the type specimen of this mineral.

Properties

Luster
Vitreous
Streak
Pale blue-green
Density
4.31
Cleavage
Perfect on {001}
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of erikapohlite is based on its unique mode of occurrence – blue-green, bladed crystals forming radial aggregates. The key is also the location of discovery (type locality) and co-occurrence with characteristic secondary minerals of the oxidation zone. ## Differentiation from Similar Minerals It can be confused with other secondary copper arsenates of similar color, such as olivenite or conichalcite. However, it is distinguished by its characteristic bladed crystal habit and radial aggregates. Final differentiation from visually similar, rare minerals requires advanced chemical (EDS) and X-ray (XRD) analyses. ## Crystal Forms It forms thin, bladed crystals, elongated along the [010] axis and flattened parallel to {001}. These crystals combine into radial, spherical aggregates and rosettes.

Geological environment

## Genesis Erikapohlite is a secondary mineral that forms in the oxidation zones of polymetallic deposits. At the type locality, it formed in vugs within hematite-quartz veins cutting Devonian shales. Its formation is a result of the weathering of primary ore minerals, mainly chalcopyrite and tennantite, which supplied copper and arsenic. ## Mineral Associations This mineral co-occurs with other rare secondary minerals. At the type locality, it was found in association with kottigite, agardite-(Y), gartrellite, olivenite, conichalcite, malachite, azurite, as well as quartz and hematite. ## Localities The only confirmed occurrence of erikapohlite in the world is its type locality: the dump of the Maria-Josefa mine, Essershausen, Weilburg, Hesse, Germany.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, the quality of a specimen is primarily determined by the richness and aesthetics of the crystal aggregates. The most valued specimens are those with well-formed, undamaged rosettes or radial clusters of intense, blue-green color, clearly contrasting with the host rock. Good contrast with the matrix and the presence of rare associated minerals are also important.

Care and storage

## Cleaning Due to its extreme rarity and delicacy, erikapohlite specimens should not be cleaned mechanically or chemically. Any contaminants, such as dust, should only be removed using compressed air from a safe distance. ## What to Avoid Avoid contact with water, acids, detergents, and any other chemicals. The crystals are very brittle and sensitive to mechanical damage. Also avoid exposure to high temperatures and sudden temperature changes. ## Storage Specimens should be stored in stable conditions, in closed, padded "micromount" boxes to protect them from dust, moisture, and physical damage. They are not suitable for display outside specialized containers.

Sources

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