Johanngeorgenstadtite

Chemical formula: Ni<sup>2+</sup><sub>4.5</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>3</sub>

Johanngeorgenstadtite is an extremely rare nickel arsenate, forming light green, platy crystals at a historical deposit in Saxony.

## Characteristics Johanngeorgenstadtite is a very rare secondary mineral from the arsenate group. It occurs as small aggregates, composed of thin, platy or bladed crystals, which often arrange themselves into rosette-like forms. Its characteristic feature is a vivid, light green to apple-green color. Due to the small size of the crystals, it is a typical micromount mineral, requiring magnification for observation. ## Physical Properties Johanngeorgenstadtite crystals exhibit a vitreous luster and are translucent. The mineral is characterized by perfect cleavage in one plane, which accounts for its platy appearance. Hardness has not been precisely determined due to the small size and fragility of the crystals. The density calculated based on chemical composition and crystal structure is 4.81 g/cm³. ## Colors and Varieties This mineral occurs in shades of green – from pale green, through apple-green, to yellowish-green. No varieties have been distinguished. ## History and Name The mineral's name comes from its discovery locality – the historic mining town of Johanngeorgenstadt in the Ore Mountains (Saxony, Germany). It was officially recognized as a new mineral species by the International Mineralogical Association (IMA) in 2022 (IMA 2022-085). ## Uses Johanngeorgenstadtite has no industrial application. It is of purely scientific and collector's interest as a very rare and recently described mineral.

Properties

Luster
Vitreous
Streak
Pale green
Density
4.81
Cleavage
Perfect on {0001}
Transparency
Translucent
Crystal system
Trigonal

Diagnostic features

## Identification Johanngeorgenstadtite can be preliminarily identified by its characteristic apple-green color, vitreous luster, and the form of thin, platy crystals forming aggregates. A key clue is its occurrence in association with other nickel, arsenic, and bismuth minerals at its known locality. ## Differentiation from Similar Minerals It can be confused with other secondary nickel arsenates, such as annabergite or aerugite. Annabergite typically forms acicular crystals and fibrous aggregates, rather than platy ones. Aerugite usually has a darker, bluish-green or blackish-green color. Definitive and certain differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS). ## Crystal Forms It forms thin, platy or bladed crystals with a hexagonal outline. These crystals usually occur as rosette-like, radial, or irregular aggregates on the surface of the host rock.

Geological environment

## Genesis It is a secondary mineral, forming in the oxidation zone of polymetallic, hydrothermal ore veins. It forms as a result of weathering and alteration of primary minerals containing nickel and arsenic, such as nickeline. ## Mineral Associations At the type locality, johanngeorgenstadtite co-occurs with minerals such as native bismuth, bismutite, bunsenite, and aerugite. ## Localities The only confirmed occurrence of this mineral in the world is its type locality – the area of shaft 371 of the former "Einigkeit" mine in Johanngeorgenstadt, Saxony (Germany).

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of specimens of this extremely rare mineral is primarily assessed based on the richness and aesthetics of the crystal aggregates. Most valued are samples with well-formed, distinct platy crystals, forming dense coatings on a small rock matrix. Association with other rare minerals adds additional value. ## Popular Localities Specimens come exclusively from one place in the world – the historic mining district of Johanngeorgenstadt in the German Ore Mountains.

Care and storage

## Cleaning Specimens should only be dry-cleaned, using a soft brush or a stream of compressed air to remove dust. Avoid contact with water and any chemical agents that could damage the delicate crystals. ## What to Avoid The mineral is very brittle and susceptible to mechanical damage, so avoid shocks, friction, and ultrasonic cleaning. As an arsenate, it is toxic – avoid inhaling dust and wash hands after any contact with the specimen. ## Storage It is recommended to store specimens in sealed "micromount" boxes, which protect against dust, moisture, and mechanical damage. Each specimen should be appropriately labeled with toxicity information.

Sources

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