Krupičkaite

Chemical formula: Cu₂+₆[As₅+O₃(OH)]₆·₈H₂O

Krupičkaite is a very rare, secondary copper arsenate with a characteristic blue-green color, forming microscopic, acicular crystals.

## Characteristics Krupičkaite is a hydrated copper arsenate, occurring as very small, acicular or bladed crystals, which rarely exceed 0.2 mm in length. These crystals form radial or chaotic aggregates, as well as thin coatings and crusts on the host rock. Due to the microscopic size of the crystals, its visual features are difficult to observe without magnification. ## Physical Properties This mineral is characterized by a vitreous luster and is transparent to translucent. Its Mohs hardness is estimated at 3-4, making it relatively soft. The density calculated based on the chemical formula and unit cell parameters is 3.43 g/cm³. ## Colors and Varieties Krupičkaite has a characteristic blue-green or greenish-blue color. No varieties have been distinguished. ## History and Name The mineral was approved by the IMA in 2019. Its name honors the Czech mineral collector and philanthropist, Jiří Krupička (1913-2014), for his contribution to the preservation of Czech and Slovak mineralogical specimens. It was discovered in the dumps of the historic Geister mine in Rovnost, in the Jáchymov area of the Czech Republic. ## Uses Krupičkaite has no industrial application. It is solely an object of scientific and collecting interest, sought after by collectors specializing in rare minerals or arsenate group minerals.

Properties

Mohs hardness: 3-4
Luster: Vitreous
Streak: Light green
Density: 3.43
Cleavage: Good on {100}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Triclinic

Diagnostic features

## Identification Identification of krupičkaite is primarily based on its characteristic form – tiny, acicular crystals forming radial aggregates of a blue-green color. The locality (oxidation zones of polymetallic deposits) and co-occurrence with other secondary copper and arsenic minerals are also crucial. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD) or Raman spectroscopy. ## Distinguishing from Similar Minerals Krupičkaite can be confused with other secondary, acicular copper arsenates, such as geminite, lindackerite, olivenite, or cyanotrichite. Distinguishing it from these minerals with the naked eye is practically impossible and requires specialized laboratory tests. Krupičkaite is chemically and structurally related to geminite. ## Crystal Forms The mineral forms very small, elongated, acicular or bladed crystals, usually grouped into radial, stellate, or chaotic aggregates. It also occurs as thin coatings and crusts.

Geological environment

## Genesis Krupičkaite is a secondary mineral, formed in the oxidation (weathering) zones of polymetallic ore deposits rich in copper and arsenic. It forms as a result of reactions of percolating waters through rocks, interacting with primary ore minerals such as chalcopyrite and arsenopyrite, under conditions of low temperature and pressure. ## Mineral Associations At the type locality (Jáchymov, Czech Republic), krupičkaite co-occurs with geminite, lavendulan, gypsum, chalcanthite, brochantite, devilline, malachite, azurite, erythrite, annabergite, and quartz. ## Localities The only confirmed and described occurrence of krupičkaite in the world is its type locality: the historic Geister mine (Rovnost I shaft) in Jáchymov, in the Karlovy Vary region of the Czech Republic.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of krupičkaite specimens is assessed based on the richness and aesthetics of the crystal aggregates. The most prized specimens are those with well-formed, radial clusters of acicular crystals, with an intense, blue-green color, contrasting with the rock matrix. Due to the microscopic nature of the mineral, the quality of the specimen observed under magnification is crucial. ## Popular Localities The only source of krupičkaite specimens is its type locality in Jáchymov, Czech Republic. Material from this location is extremely rare and sought after by specialized collectors of systematic minerals and micromounts.

Care and storage

## Cleaning Krupičkaite specimens are extremely delicate and consist of microscopic crystals. They should not be cleaned mechanically or chemically. Any attempts at cleaning may lead to irreversible damage to the aggregates. If dust removal is necessary, it can be done very carefully with a soft brush or a photographic air blower, avoiding direct contact with the crystals. ## What to Avoid Avoid contact with water, acids, bases, and any solvents. The mineral is sensitive to changes in temperature and humidity. It should not be heated or exposed to direct sunlight, which can cause dehydration and color change. ## Storage Specimens should be stored in stable conditions, preferably in closed, padded "micromount" boxes, which protect them from dust, mechanical damage, and sudden changes in humidity. Exposure should be away from heat and light sources.

Sources

IMA Mineral List (CNMNC)