Cobaltaustinite
Chemical formula: CaCo<sup>2+</sup>As<sup>5+</sup>O<sub>4</sub>(OH)
A rare calcium cobalt arsenate, forming characteristic pink to purplish-pink, small crystals in the oxidation zones of Co-As deposits.
Description
## Characteristics Cobaltaustinite is an arsenate belonging to the adelite-descloizite group, being the cobalt analogue of austinite. It forms small crystals, usually not exceeding 1-2 mm, with a tabular, short-prismatic, or acicular habit. It typically occurs as radial aggregates, rosettes, or crusts and drusy coatings. Its most recognizable feature is its intense, attractive color. ## Physical Properties This mineral is characterized by a hardness ranging from 4-4.5 on the Mohs scale, making it relatively brittle. It has a vitreous luster, approaching adamantine on some surfaces. It is transparent to translucent. Its density is approximately 4.16 g/cm³, which is a significant value, typical for heavy metal arsenates. ## Colors and Varieties Cobaltaustinite exhibits colors from pink, through reddish-pink, to purplish-pink and purple. The intensity and hue depend on the cobalt content. No named varieties are distinguished, and classification is based solely on chemical composition. ## History and Name The mineral's name refers to its chemical composition – the dominance of cobalt – and its structural similarity to austinite. It was first described in 1986 by J.L. Jambor and co-workers based on specimens from the Aghbar mine in the Bou Azzer district, Morocco. ## Uses Cobaltaustinite has no industrial applications. However, it is a valued and sought-after collector's mineral due to its rarity, intense color, and attractive forms of occurrence.
Diagnostic features
## Identification Key diagnostic features of cobaltaustinite are its intense pink to purple color, relatively high hardness (for a secondary arsenate), and co-occurrence with other cobalt and arsenic minerals. Its characteristic forms of occurrence as small, radial aggregates and crusts are also distinctive. ## Distinguishing from Similar Minerals Cobaltaustinite is sometimes confused with erythrite (cobalt bloom). However, erythrite is much softer (1.5-2.5 on the Mohs scale), has perfect cleavage in one direction, and often forms acicular crystals in fan-shaped aggregates. Another similar mineral is roselite, which also crystallizes in the monoclinic system (cobaltaustinite in orthorhombic) and has a slightly different chemical composition. ## Crystal Forms It crystallizes in the orthorhombic system. It most often forms small, tabular or short-prismatic crystals, which rarely occur individually. They usually coalesce into radial or fan-shaped aggregates, and also form dense, drusy crusts on the host rock.
Geological environment
## Genesis Cobaltaustinite is a secondary mineral, formed in the oxidation (weathering) zones of hydrothermal ore deposits rich in cobalt and arsenic. It forms as a result of the alteration of primary cobalt arsenides and sulfoarsenides, such as skutterudite or cobaltite. ## Mineral Associations It most often co-occurs with other secondary arsenates, such as erythrite, roselite, talmessite, and adamite. It is also accompanied by gangue minerals, mainly dolomite, quartz, and calcite, as well as remnants of primary minerals. ## Localities The most important and best-known locality for cobaltaustinite in the world is the Bou Azzer district in Morocco, especially the Aghbar and Tamdrost mines. The best collector's specimens come from there. This mineral has also been reported in Schneeberg, Germany, and in several other less significant localities worldwide.
Rarity
Rare
Collector aspects
## Quality Criteria The most highly valued cobaltaustinite specimens are characterized by an intense, saturated, purplish-pink color. The size and development of the crystals are important, although even well-formed microcrystals are desirable. The attractiveness of a specimen is enhanced by rich coverage of the rock matrix and contrasting associations with other minerals, for example, with white dolomite. ## Popular Localities Specimens from the Bou Azzer district in Morocco are by far the most sought after by collectors. They are considered the global standard for this mineral.
Care and storage
## Cleaning Cobaltaustinite specimens should be cleaned very carefully, preferably dry using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Due to its arsenic content, avoid inhaling dust during cleaning, and wash hands thoroughly after contact with the mineral. ## What to Avoid The mineral is sensitive to acids, which can damage it. Ultrasonic cleaners and mechanical cleaning, which could scratch or destroy delicate crystals, should be avoided. It should not be heated or exposed to prolonged strong sunlight, although it is considered stable under normal conditions. ## Storage It is recommended to store specimens in closed, padded boxes or display cases to protect them from dust and mechanical damage. Each specimen should be labeled with a warning about its toxicity (arsenic content).