Clinoatacamite

Chemical formula: Cu₂+₂Cl(OH)₃

Clinoclasite, a rare polymorph of atacamite, is a secondary copper mineral forming characteristic, dark-green crystals with a vitreous luster.

## Characteristics Clinoclasite is a mineral from the halide group, belonging to the polymorphs of atacamite, which means it has the same chemical composition (Cu₂Cl(OH)₃) but a different crystal structure. It typically forms small, prismatic or tabular crystals, often gathered into radial, fan-shaped, or spherical aggregates. Specimens have an intense, dark-green to blackish-green color and an attractive, vitreous luster, making them prized by collectors. ## Physical Properties This mineral is characterized by a hardness of 3 on the Mohs scale, making it relatively soft. Its density ranges from 3.76 to 3.78 g/cm³. Crystals exhibit perfect cleavage in one direction. The luster is vitreous, and the mineral can be transparent to translucent, especially in the case of smaller crystals. ## Colors and Varieties Clinoclasite occurs in shades from dark-green to almost black. No named color or commercial varieties are distinguished; its name is unequivocally linked to its composition and crystal structure. ## History and Name The mineral's name refers to its monoclinic crystallographic system and chemical similarity to atacamite. It was first described as a distinct mineral species in 1996 by Peter A. Williams and collaborators, following studies of specimens from the Chuquicamata mine in Chile, which is its type locality. ## Uses Clinoclasite has no industrial application. It is a mineral of purely scientific and collectible significance, sought after for its attractive crystal forms and intense color.

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: Green
Density: 3.76 - 3.78
Cleavage: Perfect on {010}
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Clinoclasite can be identified by its characteristic dark-green color, vitreous luster, and typical forms of occurrence – radial or fan-shaped aggregates of small, prismatic crystals. A light-green streak is also an important diagnostic feature. ## Distinguishing from Similar Minerals Clinoclasite is most often confused with its polymorphs: atacamite and paratacamite. Atacamite usually forms longer, columnar crystals with a slightly lighter shade of green. Paratacamite often occurs as microcrystalline aggregates or rhombohedral crystals. Final differentiation of these three minerals requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Clinoclasite crystals are usually small, with a prismatic or tabular habit. They most often form striking aggregates: rosette-like, radial, fan-shaped, and also spherulitic (spherical) clusters. Single, well-formed crystals are less common.

Geological environment

## Genesis Clinoclasite is a secondary mineral, forming in the oxidation zones of copper ore deposits. It forms in dry, desert climates as a result of saline waters or aerosols acting on primary copper minerals. It can also form as a product of volcanic exhalations. ## Mineral Associations This mineral often co-occurs with other secondary copper minerals, especially its polymorphs – atacamite and paratacamite. It is also accompanied by malachite, brochantite, anglesite, calcite, and iron oxides (e.g., hematite). ## Localities The most important and well-known clinoclasite localities in the world are in Chile, particularly in the Antofagasta region (Chuquicamata, La Farola mines). It also occurs in Australia (Broken Hill mine, New South Wales), Greece (Lavrion region mines), Italy (Vesuvius), and the USA (Arizona).

Rarity

Rare

For collectors

## Quality Criteria Specimens with well-formed, lustrous crystals forming aesthetic, radial or fan-shaped aggregates are most valued by collectors. An intense, dark-green color and absence of damage are important. Contrast with a light matrix also enhances the specimen's attractiveness. ## Popular Localities The best specimens in the world are considered to be those from mines in the Antofagasta region of Chile, especially from the Chuquicamata and La Farola mines. These provide specimens with exemplary crystal development and intense color.

Care and storage

## Cleaning Clinoclasite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. After wet cleaning, the specimen should be immediately and thoroughly dried. ## What to Avoid Contact with acids and other chemicals, which can easily damage the mineral, should be strictly avoided. Clinoclasite is soft and brittle, so it must be protected from impacts and scratching. It should not be heated or exposed to prolonged moisture. ## Storage It is recommended to store specimens in separate, padded collector boxes to prevent mechanical damage and contact with other minerals. It should be protected from dust and moisture by storing it in stable room conditions.

Sources

IMA Mineral List (CNMNC)