Bobkingite

Chemical formula: Cu<sup>2+</sup><sub>5</sub>Cl<sub>2</sub>(OH)<sub>8</sub>·2H<sub>2</sub>O

Bobkingite is a rare copper hydroxychloride with a characteristic azure color, forming small, spherical aggregates and rosettes.

## Characteristics Bobkingite is a secondary copper mineral that visually appears as crusts and coatings up to 1 mm thick. It forms characteristic, small aggregates in the form of rosettes or hemispherical clusters, composed of thin, bladed crystals. Its diameter rarely exceeds 0.5 mm, making it a typical micromount mineral. ## Physical Properties Bobkingite crystals exhibit a vitreous luster and are translucent. The mineral's hardness is low, estimated at about 3 on the Mohs scale, making it susceptible to scratching. ## Colors and Varieties This mineral is characterized by an attractive, uniform color, described as azure, sky blue, or "robin's egg blue." No color varieties or commercial names are distinguished. ## History and Name Bobkingite was recognized as a new mineral by the IMA in 1999. Its name honors Robert J. King (1923–2000), a British mineralogist, collector, and curator of collections at the Leicester Museum. It was discovered in the Esperanza mine in Aroma Province, Bolivia. ## Applications Due to its rarity and occurrence in small clusters, bobkingite has no industrial applications. It is solely an object of scientific and collecting interest, being a valued acquisition for specialized collections of rare minerals and micromounts.

Properties

Mohs hardness
~3
Luster
Vitreous
Streak
Light blue
Cleavage
Perfect on {001}
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of bobkingite include its azure color, vitreous luster, and typical forms of occurrence as small rosettes and hemispherical aggregates. Its environment of occurrence – oxidation zones of copper deposits – is also crucial for identification. ## Distinguishing from Similar Minerals Bobkingite can be confused with other blue secondary copper minerals, such as chrysocolla, aurichalcite, or chalcanthite. Chrysocolla usually has a waxy or earthy luster and occurs in amorphous forms. Aurichalcite forms acicular crystals with a pearly luster and often occurs in association with hydrozincite. Chalcanthite is water-soluble. Definitive differentiation often requires advanced analytical methods. ## Crystal Forms Bobkingite crystallizes in very small, thin, bladed crystals. These crystals form radial aggregates, arranging themselves into rosettes or hemispheres that grow on the host rock or other minerals.

Geological environment

## Genesis Bobkingite is a secondary mineral, forming in the oxidation zones of polymetallic, hydrothermal ore deposits. It forms as a result of weathering and alteration of primary copper minerals, such as chalcopyrite, in the presence of chloride-rich solutions. ## Mineral Associations This mineral co-occurs with other secondary copper minerals. Its associates include brochantite, libethenite, pseudomalachite, and chrysocolla. ## Localities The most important and type locality for bobkingite is the Esperanza mine, Laurani, in the La Paz Department, Bolivia. It has also been identified in the historic Great Orme copper mine in Llandudno, Wales (United Kingdom).

Rarity

Very rare

For collectors

## Quality Criteria As a micromount mineral, bobkingite is primarily evaluated based on the richness of the specimen – the denser and more numerous the aggregates on the rock matrix, the better. Well-formed, undamaged rosettes with an intense, azure color are highly prized. Contrast with associated minerals also enhances visual appeal. ## Popular Localities Specimens from the type locality, the Esperanza mine in Bolivia, are the most well-known and sought after by collectors specializing in rare minerals.

Care and storage

## Cleaning Bobkingite specimens are very delicate and should be handled with extreme care. For dust removal, it is best to use a soft brush or a photographic air blower. Wet cleaning should be avoided; if absolutely necessary, distilled water can be used, but contact with it should be as brief as possible. ## What to Avoid The mineral is sensitive to chemicals, especially acids, which can damage it. Ultrasonic cleaners, high temperatures (risk of dehydration), and direct, intense sunlight should be avoided. Due to its low hardness, it is very susceptible to mechanical damage and abrasion. ## Storage It is recommended to store specimens in sealed containers, preferably in micromount boxes, which protect against dust, moisture, and physical damage. Touching the crystal surfaces should be avoided.

Sources

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