Kernowite

Chemical formula: Cu<sup>2+</sup><sub>2</sub>Fe<sup>3+</sup>(As<sup>5+</sup>O<sub>4</sub>)(OH)<sub>4</sub>·4H<sub>2</sub>O

Kernowite is a very rare, secondary copper and iron arsenate, distinguished by its characteristic green color and acicular crystals.

## Characteristics Kernowite is a hydrated copper and iron arsenate belonging to the olivenite group. It occurs as radial aggregates or clusters of small, acicular crystals up to 1 mm long. Its most characteristic feature is an intense green color, often with a turquoise or emerald hue. It is a secondary mineral, forming in the oxidation zones of ore deposits. ## Physical Properties Kernowite crystals exhibit a vitreous luster. The mineral is brittle. Due to the small size of the crystals, precise determination of many physical properties, such as hardness or density, is difficult. ## Colors and Varieties Kernowite occurs in a characteristic green color, which can take on various shades – from emerald green to bluish-green. No varieties have been distinguished. ## History and Name The mineral's name comes from the word "Kernow," which means Cornwall in the Cornish language – a region in Great Britain where its type locality is situated. It was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2020. The specimen on which it was described was collected approximately 220 years earlier and had been stored in the collections of the Natural History Museum in London, mistakenly identified as liroconite. ## Uses Due to its extreme rarity and small size, kernowite has no industrial applications. It is solely an object of scientific and collecting interest.

Properties

Luster
Vitreous
Streak
Light green
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Kernowite can be identified by its characteristic green color, vitreous luster, and mode of occurrence – typically as radial aggregates composed of small, acicular crystals. Key to its identification is its genesis (oxidation zone) and co-occurrence with other secondary copper minerals. ## Distinguishing from Similar Minerals It can be confused with other green copper arsenates, such as olivenite or cornwallite. Olivenite often forms more massive or prismatic crystals. Cornwallite usually occurs in botryoidal or reniform aggregates. Accurate differentiation of these minerals often requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS). ## Crystal Forms Kernowite crystals are elongated, acicular, or bladed. They usually form radial or stellate aggregates, as well as haphazard clusters on the surface of the host rock (matrix).

Geological environment

## Genesis Kernowite is a secondary mineral, forming in the oxidation zones (gossans) of polymetallic deposits rich in copper and arsenic. It forms as a result of the weathering of primary sulfides and arsenides, such as chalcopyrite and arsenopyrite. ## Mineral Associations It most commonly co-occurs with other secondary minerals. In its type locality (Wheal Gorland mine), it was found in association with liroconite, cornwallite, olivenite, as well as quartz, chalcophyllite, and mansfieldite. ## Localities The only confirmed and described locality for kernowite in the world is the historic Wheal Gorland mine in St Day, Cornwall (United Kingdom).

Rarity

Extremely rare

For collectors

## Quality Criteria The most highly prized kernowite specimens are those with rich, well-formed, radial aggregates of acicular crystals of an intense, emerald-green color. An aesthetic quartz matrix and the presence of rare associated minerals, especially liroconite, are also important. Due to the microscopic nature of the crystals, specimens are evaluated under magnification. ## Popular Localities The only source of specimens is the historic Wheal Gorland mine in Cornwall. Material comes exclusively from old collections, as the mine has long been inactive, and the mine dumps have been largely reclaimed. New finds are practically impossible.

Care and storage

## Cleaning Kernowite specimens are extremely delicate. Cleaning should be kept to an absolute minimum. If necessary, a soft brush can be used to remove dust or the specimen can be very carefully blown with compressed air from a safe distance. ## What to Avoid Contact with water, chemicals, acids, and detergents must be strictly avoided. Ultrasonic cleaners should not be used. The mineral is sensitive to shocks and impacts, which can destroy the tiny crystals. It should be protected from high temperatures and sudden changes in temperature. ## Storage Kernowite specimens are best stored in enclosed, padded "micromount" boxes to protect them from dust, mechanical damage, and moisture. Display should take place under stable conditions, away from direct sunlight.

External references

Sources

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