Edwardsite

Chemical formula: Cu<sup>2+</sup><sub>3</sub>Cd<sup>2+</sup><sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>·4H<sub>2</sub>O

Edwardsite is a very rare hydrated copper cadmium sulfate, forming blue, spherical aggregates of fine, platy crystals.

## Characteristics Edwardsite is a mineral from the sulfate group, chemically classified as a hydrated copper cadmium sulfate. It occurs as small, spherical or hemispherical aggregates, reaching up to 0.5 mm in diameter. These aggregates are composed of extremely fine, platy or acicular crystals, which rarely exceed 50 micrometers in length and a few micrometers in thickness. Due to their size, individual crystals are only visible under high magnification. ## Physical Properties Edwardsite crystals exhibit a vitreous luster. The mineral is translucent. Its hardness and density have not been precisely measured due to the small size and fragility of the samples; however, the density calculated based on the chemical formula and unit cell parameters is 3.46 g/cm³. ## Colors and Varieties This mineral is characterized by a uniform, light blue or sky blue color. No varieties have been distinguished. ## History and Name Edwardsite was discovered in the dumps of the Silver Hill Mine in Davidson County, North Carolina, USA. It was described in 2010 by Anthony R. Kampf and colleagues. The mineral is named in honor of Robert "Bob" W. Edwards (b. 1953), an American mineral collector and researcher, in recognition of his contributions to mineralogy, especially of North Carolina.

Properties

Luster
Vitreous
Streak
Light blue
Density
3.46
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of edwardsite include its blue color, specific occurrence as small, spherical aggregates, and mineral associations. Due to its size, positive identification requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS). ## Distinguishing from Similar Minerals Edwardsite can be confused with other secondary copper sulfates of similar color and form, such as chalcanthite, ktenasite, or serpierite. It differs from chalcanthite by its insolubility in cold water. Distinguishing it from ktenasite or serpierite based on visual characteristics is practically impossible and requires specialized instrumental analysis. ## Crystal Forms The mineral forms very fine, platy or acicular crystals that combine into radial, spherical, or hemispherical aggregates.

Geological environment

## Genesis Edwardsite is a secondary mineral, formed in the oxidation zone of ore deposits. It forms as a result of the weathering of primary minerals containing copper and cadmium, such as chalcopyrite and sphalerite (cadmian variety). It forms under low-temperature conditions, in voids and fissures in rocks. ## Mineral Associations At the type locality (Silver Hill Mine), edwardsite occurs in association with other rare secondary minerals, such as chalcanthite, gypsum, goethite, hemimorphite, ktenasite, serpierite, and the newly discovered silverhillite. ## Localities The only confirmed locality for edwardsite in the world is its type locality – the dumps of the former Silver Hill Mine, in the Cid District, Davidson County, North Carolina, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" mineral, edwardsite is primarily evaluated based on the quality and aesthetics of microscopic specimens. The most prized are well-formed, undamaged spherical aggregates of intense blue color, contrastingly set on a rock matrix. The presence of associated minerals is also important, as it enhances the scientific and aesthetic value of the specimen. ## Popular Localities The only source of edwardsite specimens is the Silver Hill Mine in North Carolina, USA. Material from this locality is highly sought after by collectors specializing in rare minerals and "micromount" specimens.

Care and storage

## Cleaning Edwardsite specimens are extremely delicate and small. Mechanical cleaning is inadvisable and can lead to the destruction of aggregates. If absolutely necessary, compressed air can be carefully used from a safe distance to remove loose dust. Contact with water, which can dissolve or damage the mineral, should be avoided. ## What to Avoid Contact with water, acids, detergents, and other chemicals must be strictly avoided. The mineral is sensitive to changes in humidity and temperature. It should not be heated or exposed to direct sunlight. Vibrations and impacts can cause fragile aggregates to disintegrate. ## Storage It is recommended to store specimens exclusively in specialized, sealed "micromount" boxes that protect against dust, mechanical damage, and sudden environmental changes. Display should be in stable conditions, away from sources of vibration and direct light.

External references

Sources

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