Chenevixite

Chemical formula: Cu₂+Fe₃+(As₅+O₄)(OH)₂

Chenevixite is a rare copper iron arsenate, forming characteristic olive-green aggregates.

## Characteristics Chenevixite is a hydrated copper iron arsenate. It most commonly occurs as microcrystalline, compact, or earthy masses, as well as spherical, reniform, or botryoidal aggregates. It rarely forms discernible crystals, which are usually in the form of tiny, monoclinic needles or tablets. Its characteristic feature is an olive-green, dark green, or yellowish-green color. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3.5-4.5. It has a dull, earthy luster, and in the case of more compact aggregates, a weak resinous luster. It is opaque or at most translucent on thin edges. Its density ranges from 3.93 to 4.0 g/cm³. ## Colors and Varieties Chenevixite occurs in various shades of green, from olive and dark green to yellow-green and black-green. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral's name honors the Irish chemist Richard Chenevix (1774-1830), who was the first to perform a chemical analysis of a similar material from Cornwall. The mineral was formally described and named by Adam in 1866. ## Uses Chenevixite has no industrial application. It is of purely scientific and collector's interest, being an interesting secondary mineral from the oxidation zones of copper and arsenic ores.

Properties

Mohs hardness: 3.5-4.5
Luster: Dull to weakly resinous
Streak: Yellowish-green
Density: 3.93 - 4.0
Cleavage: None
Fracture: Uneven to conchoidal
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Chenevixite is primarily identified by its characteristic olive-green color, dull or earthy appearance, and typical forms of occurrence – spherical, reniform, or compact masses. Its presence in the oxidation zones of copper and arsenic deposits is a key indicator. ## Distinguishing from Similar Minerals It can be confused with other green secondary copper minerals, such as malachite, pseudomalachite, olivenite, or cornwallite. It is distinguished from malachite by its lack of reaction with hydrochloric acid. Distinguishing it from olivenite and cornwallite often requires chemical analysis (EDS) to confirm the presence of iron. Its lower hardness distinguishes it from many similar minerals. ## Crystal Forms Well-formed crystals are very rare. It most often occurs as microcrystalline, radial, spherical (spherulitic), botryoidal, and reniform aggregates. It also forms massive, earthy, and crust-like coatings.

Geological environment

## Genesis Chenevixite is a secondary mineral, formed in the oxidation zones (gossans) of hydrothermal copper and arsenic ore deposits, especially chalcopyrite and enargite. It forms as a result of the weathering of primary sulfides and arsenides in the presence of oxygen-rich waters. ## Mineral Associations It often co-occurs with other minerals from the oxidation zone, such as malachite, azurite, olivenite, cornwallite, tyrolite, chalcophyllite, quartz, goethite, and other iron oxides. ## Localities Important historical and classic localities include mines in Cornwall (Great Britain), from which the first studied specimens originated. Significant finds also come from the Tintic mine in Utah (USA), Tsumeb in Namibia, and the Cobar region in New South Wales (Australia). It also occurs in many places in Chile, Germany (Saxony), and France.

Rarity

Rare

For collectors

## Quality Criteria The most prized by collectors are specimens with well-formed, even microscopic, crystals or those forming aesthetic, spherical or reniform aggregates of intense, olive-green color. Contrast with the rock matrix and associations with other rare secondary minerals are also important. Specimens from classic, historical localities, such as Cornwall or Tintic, are particularly sought after. ## Popular Localities The most well-known collector's specimens come from historical mines in the St Day district in Cornwall (Great Britain), the Mammoth and Gold Hill mines in the Tintic district, Utah (USA), and the Tsumeb mine (Namibia).

Care and storage

## Cleaning Chenevixite specimens should be cleaned very carefully, preferably dry using a soft brush or compressed air. If necessary, a damp cotton swab with distilled water can be used, but avoid saturating the specimen, especially if it is porous or mounted on a sensitive substrate. ## What to Avoid Avoid contact with acids and other chemicals that may react with arsenates. The mineral is brittle and sensitive to impact and abrasion. It should not be heated or cleaned in ultrasonic cleaners. ## Storage Specimens should be stored in separate, padded boxes or display cases to prevent scratches and mechanical damage. Protection from dust and moisture is recommended. Due to its arsenic content, hands should be washed after handling the mineral.

Sources

IMA Mineral List (CNMNC)