Anorthoroselite

Chemical formula: Ca₂Co₂+(As₅+O₄)₂·₂H₂O

A rare calcium cobalt arsenate, forming small, pinkish-red crystals, which is the triclinic analog of roselite.

## Characteristics Anorthoroselite is a hydrated calcium cobalt arsenate belonging to the roselite group. It forms small, tabular or prismatic crystals, which rarely occur individually. It typically forms druses and crusts covering the host rock or filling its fissures. It often occurs as radial or spherical aggregates with an intense, pinkish-red to pink color. ## Physical Properties This mineral is characterized by a vitreous luster and is transparent to translucent. Its Mohs hardness is approximately 3.5, making it relatively soft and brittle. The density is significant, around 3.71 g/cm³. ## Colors and Varieties Anorthoroselite occurs in characteristic shades of pink and red, from pale pink to intense, pinkish-red. The color is its main diagnostic feature and results from the presence of cobalt ions in the crystal structure. No named varieties are distinguished. ## History and Name The mineral's name, approved in 1988, refers to its relationship with roselite and its triclinic (anorthic) crystallographic system. Anorthoroselite is the triclinic dimorph of monoclinic roselite, meaning both minerals have the same chemical composition but crystallize in different systems. ## Applications Due to its rarity, small crystal sizes, and attractive color, anorthoroselite is a mineral of purely scientific and collectible interest.

Properties

Mohs hardness: 3.5
Luster: Vitreous
Streak: Light pink
Density: 3.71
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Transparent to Translucent to transparent
Crystal system: Triclinic

Diagnostic features

## Identification The key diagnostic features of anorthoroselite are its intense pinkish-red color, vitreous luster, and occurrence as small crystals forming radial aggregates and crusts. Its geological environment – oxidation zones of cobalt and arsenic ore deposits – is also an important indicator. ## Distinguishing from Similar Minerals Anorthoroselite is visually indistinguishable from roselite without advanced studies, such as X-ray diffraction (XRD). Both minerals have practically identical appearance and physical properties. It can also be confused with erythrite, which, however, usually has a more purplish-pink hue and forms acicular crystals. ## Crystal Forms Crystals are small, most often tabular or short-prismatic. They usually occur as radial or spherical aggregates, as well as druses and crusts of small, densely packed crystals.

Geological environment

## Genesis Anorthoroselite is a secondary mineral, formed in the oxidation zones of hydrothermal ore deposits containing arsenic and cobalt. It crystallizes in rock fissures and voids as a result of the weathering of primary cobalt minerals. ## Mineral Associations It most often co-occurs with minerals of similar genesis, such as roselite, erythrite, talmessite, quartz, dolomite, and cobalt-bearing calcite. ## Localities The type locality for this mineral is Schneeberg in Saxony (Germany). However, the most famous and prized collector specimens come from the renowned mining region of Bou Azzer in Morocco. It is also known from several other places in the world, including Chile.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued anorthoroselite specimens are characterized by an intense, saturated, pinkish-red color. The size and habit of the crystals forming the aggregates are important – the larger and better defined, the more valuable the specimen. Aesthetic contrast with a light matrix rock (e.g., dolomite) and the absence of damage enhance its attractiveness. ## Popular Localities The vast majority of the best anorthoroselite specimens available on the collector's market come from the Bou Azzer district in Morocco. Specimens from this locality have set the quality standard for this mineral.

Care and storage

## Cleaning Anorthoroselite specimens are delicate and should be cleaned with great care. The safest method is to use a soft brush to remove dust or canned compressed air. If necessary, the specimen can be rinsed in distilled water and then immediately and thoroughly dried. As an arsenate, it is toxic – hands should be washed after any contact with the mineral. ## What to Avoid Avoid ultrasonic cleaners, which can damage brittle crystals. The mineral is sensitive to acids, which can damage it. It should be protected from impacts and scratches due to its low hardness. Prolonged exposure to strong sunlight is not recommended. ## Storage It is recommended to store specimens in closed boxes or display cases to protect them from dust and mechanical damage. Separation from harder minerals will prevent accidental scratching.

Sources

IMA Mineral List (CNMNC)