Claraite

Chemical formula: (Cu<sup>2+</sup>,Zn<sup>2+</sup>)<sub>15</sub>(CO<sub>3</sub>)<sub>4</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)(OH)<sub>14</sub>·7H<sub>2</sub>O

A rare, secondary copper and zinc mineral with a characteristic blue color, forming small, spherical aggregates and rosettes.

## Characteristics Claraite is a hydrated copper and zinc carbonate-arsenate-sulfate, occurring as very small, acicular or bladed crystals. These crystals typically form spherical or hemispherical aggregates, rosettes, and thin coatings and crusts on rock surfaces. Due to the small size of the crystals, its features are difficult to observe with the naked eye, and specimens most often appear as clusters of tiny, blue spherules. ## Physical Properties This mineral is characterized by a hardness of about 2 on the Mohs scale, making it very soft. It has a vitreous luster, and its crystals are usually translucent. The calculated density is 3.36 g/cm³. ## Colors and Varieties Claraite occurs in a characteristic, light, blue-green or sky-blue color. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name comes from the Clara mine in the Black Forest (Baden-Württemberg, Germany), where it was discovered. It was described by Kurt Walenta and Pete J. Dunn in 1982, and the International Mineralogical Association (IMA) approved it as a new mineral in the same year. ## Uses Claraite has no industrial application. It is solely a mineral of scientific and collecting interest, valued by collectors specializing in rare minerals or minerals from specific localities (so-called "systematists").

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Pale blue
Density
3.36
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Trigonal

Diagnostic features

## Identification Claraite is primarily identified by its characteristic blue color, its occurrence in the form of small, spherical aggregates, and its discovery location (Clara mine). It reacts violently with hydrochloric acid, which is an important diagnostic feature, but destroys the sample. ## Distinguishing from Similar Minerals It can be confused with other secondary copper minerals of similar color and habit, such as aurichalcite, rosasite, cyanotrichite, or tyrolite. Aurichalcite and rosasite have similar forms but differ in chemical composition (they do not contain arsenic or sulfates). Cyanotrichite forms acicular aggregates with a more silky luster. Tyrolite has a similar color but excellent cleavage and often a pearly luster. Definitive distinction requires advanced analytical methods (e.g., XRD, EDS). ## Crystal Forms Crystals are very small, acicular or bladed, up to 0.1 mm long. They typically occur as radial or spherulitic (spherical) aggregates, rosettes, and thin coatings on other minerals.

Geological environment

## Genesis Claraite is a secondary mineral, forming in the oxidation (weathering) zones of polymetallic ore deposits rich in copper, zinc, and arsenic. It forms as a result of surface waters acting on primary ore minerals in the presence of carbonates. ## Mineral Associations It most often co-occurs with minerals such as barite, fluorite, goethite, malachite, olivenite, quartz, sphalerite, chalcopyrite, and other rare secondary minerals, especially from the arsenate and carbonate groups. ## Localities The most important and type locality is the Clara mine, Wolfach, Black Forest in Germany. This site is known for the occurrence of many rare secondary minerals. Beyond this locality, its presence has been noted in several other places worldwide, including the Cap Garonne mine in France and in small quantities in other regions of Europe.

Rarity

Very rare

For collectors

## Quality Criteria The collecting appeal of claraite specimens primarily depends on the abundance and aesthetics of the aggregates. The most prized specimens are those where the spherical clusters are numerous, well-formed, and have an intense, sky-blue color. Contrast with the rock matrix (e.g., with white barite or quartz) and the presence of other rare associated minerals are also important. Due to the microscopic size of the crystals, individual, isolated crystals are not the main criterion for evaluation. ## Popular Localities Undoubtedly, the most known and valued specimens come from the type locality - the Clara mine in Germany. Specimens from this location are the standard for this mineral and practically dominate the collector's market.

Care and storage

## Cleaning Claraite specimens are extremely delicate and sensitive. Cleaning should be kept to an absolute minimum. If necessary, a very soft brush can be used to remove loose dust particles. Water and any chemical agents should be avoided. ## What to Avoid The mineral is sensitive to acids, which cause it to effervesce violently and decompose. Contact with water, chemicals, ultrasonic cleaners, and sudden temperature changes should be avoided. As a secondary mineral, it is susceptible to changes in humid environments. ## Storage Specimens should be stored in stable conditions, in closed, dry containers or display cases, away from direct sunlight and heat sources. Due to its softness and fragility, it should be protected from shocks and contact with harder minerals.

Sources

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