Keyite

Chemical formula: (&#₉₇₂₃;₀.₅Cu²⁺₀.₅)Cu²⁺Cd²⁺Zn²⁺₂(As⁵⁺O₄)₃·H₂O

Keyite is a very rare zinc, cadmium, and copper arsenate, forming characteristic blue, radial aggregates.

## Characteristics Keyite is a hydrated zinc, cadmium, and copper arsenate, belonging to the alluaudite group. It occurs extremely rarely, forming clusters of small, prismatic crystals that often arrange themselves into radial or spherulitic aggregates. Its most characteristic feature is its intense, azure-blue color. ## Physical Properties Keyite crystals are very small, usually not exceeding 1 mm in length. This mineral is brittle and characterized by a vitreous luster. Its Mohs hardness ranges from 3 to 4, and its density is relatively high, measured at 5.65 g/cm³. ## Colors and Varieties Keyite occurs in a uniform, azure-blue color. No color varieties or commercial varieties are known. ## History and Name The mineral was discovered in the Tsumeb mine in Namibia and described in 1977 by Paul Keller, Heinz Hess, and Pete J. Dunn. The name honors Charles Locke Key (born 1935), an American mineral collector and dealer from Arizona, who provided the first samples for research and was an expert on Tsumeb minerals. ## Uses Due to its extreme rarity and microscopic crystal size, keyite has no industrial application. It is solely an object of interest for specialized mineral collectors (so-called micromounters) and scientific institutions.

Properties

Mohs hardness: 3.5-4
Color: Deep sky blue, blue
Luster: Vitreous
Streak: Pale blue
Density: 5.106
Cleavage: {001}
Fracture: Uneven
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Keyite is primarily recognizable by its unique combination of features: intense azure-blue color, formation of radial aggregates composed of small, prismatic crystals, and occurrence in the specific mineral environment of the Tsumeb mine. ## Distinguishing from Similar Minerals It can be confused with other blue arsenates from Tsumeb, such as scorodite, but scorodite usually has a different crystal habit and is vitreous to earthy. Liroconite, although similar in color, crystallizes in a different system and forms crystals of a different shape. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Crystal Forms It forms elongated, prismatic crystals, often terminated by steep faces. These crystals almost always occur in radial or spherulitic aggregates, rarely as single, overgrown crystals.

Geological environment

## Genesis Keyite is a secondary mineral that formed in the oxidation zone (gossan) of a polymetallic hydrothermal deposit in dolomitic rocks. It formed as a result of the weathering of primary sulfides (mainly tennantite) rich in zinc, copper, and arsenic, in the presence of cadmium. ## Mineral Associations It most commonly co-occurs with quartz, tennantite, galena, olivenite, prosperite, ludlockite, conichalcite, cuprite, and anglesite. It also occurs in association with other rare arsenates from Tsumeb. ## Localities The only confirmed locality of keyite in the world is its type locality – the Tsumeb mine in the Oshikoto Region, Namibia. It is an endemic mineral to this deposit.

Rarity

Very rare

For collectors

## Quality Criteria The most prized keyite specimens are those that possess well-developed, clearly visible radial aggregates of an intensely blue color, contrasting with a light matrix rock (most often quartz). The size of the aggregates and the richness of their occurrence on the matrix significantly increase the value of the specimen. Due to the microscopic nature of the mineral, the aesthetics of the entire cluster are crucial. ## Popular Localities All known and valued keyite specimens come from a single location in the world – the Tsumeb mine in Namibia, which closed in 1996. This means that new specimens no longer appear on the market, and all available ones come from old collections.

Care and storage

## Cleaning Keyite specimens should be cleaned with the utmost care, exclusively using a soft brush to remove dust. Due to its brittleness and potential reactivity, contact with water and any chemical agents should be avoided. ## What to Avoid Ultrasonic cleaners, chemical agents (acids, bases, solvents), and sudden temperature changes must be absolutely avoided. The mineral is brittle, so it should be protected from impacts and vibrations. ## Storage Keyite specimens, usually in the form of micromounts, should be stored in stable conditions, in sealed "micromount" boxes that protect them from dust, mechanical damage, and moisture.