Cobaltkieserite
Chemical formula: Co<sup>2+</sup>S<sup>6+</sup>O<sub>4</sub>·H<sub>2</sub>O
Cobaltkieserite is a rare, monoclinic cobalt sulfate, forming tiny, pink crystals and coatings.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- Pale pink
- Density
- 3.08
- Cleavage
- Good on {111}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Key diagnostic features include its intense pink color, occurrence as fine crystals or coatings, and specific geological environment – oxidation zones of sulfide deposits. It reacts with water. Final confirmation requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS). ## Distinguishing from Similar Minerals Cobaltkieserite can be confused with other pink, secondary cobalt minerals, such as: - **Erythrite (Cobalt bloom, Co₃(AsO₄)₂·8H₂O):** Usually forms larger, acicular or radial aggregates and is an arsenate, not a sulfate. - **Bieberite (CoSO₄·7H₂O):** Is much more hydrated and less stable in dry air, often forming stalactites or efflorescences. Cobaltkieserite can form from its dehydration. - **Spherocobaltite (CoCO₃):** Has higher hardness (3.5-4) and reacts with acids, releasing carbon dioxide. ## Crystal Forms Crystals are very small, tabular or short-prismatic. They usually form rosette-like or radial aggregates, as well as fibrous clusters and earthy coatings.
Geological environment
## Genesis Cobaltkieserite is a secondary mineral formed in the oxidation (weathering) zones of ore deposits containing cobalt minerals, such as cobaltite, skutterudite, or siegenite. It forms under low humidity conditions, often as a product of dehydration of more hydrated cobalt sulfates, e.g., bieberite. ## Mineral Associations This mineral co-occurs with other secondary sulfates and arsenates. It is most often associated with: bieberite, morenosite, annabergite, erythrite, gypsum, and iron oxides (goethite, limonite). ## Localities As a rare mineral, cobaltkieserite has been identified in only a few locations worldwide. The most important include: - **"Friedrich" Mine in Steinebach/Sieg, Rhineland-Palatinate, Germany** - one of the key localities. - **"Lubin" Mine, Lower Silesia, Poland** - the place of first discovery (type locality). - **"Polkowice-Sieroszowice" Mine, Lower Silesia, Poland**. - **Gladhammar, Kalmar, Sweden**.
Rarity
Very rare
For collectors
## Quality Criteria The collector's appeal of a specimen primarily depends on the intensity and saturation of its pink color and the richness of its occurrence on the rock matrix. Specimens with clearly formed, though still microscopic, crystal rosettes, contrasting with the dark host rock, are most valued. Due to their microscopic nature, specimens are often evaluated under magnification. ## Popular Localities Specimens from German mines in the Siegerland region (e.g., Friedrich mine) and from Polish copper mines (LGOM) are the most representative for this mineral and are most commonly found in specialized collections.
Care and storage
## Cleaning Cobaltkieserite specimens are extremely delicate and sensitive to water. Mechanical cleaning is highly risky. If necessary, compressed air (from a safe distance) can be used to remove dust. Any contact with liquids should be avoided. ## What to Avoid Absolute avoidance of contact with water is crucial, as it can dissolve or damage the mineral. It should also be protected from high air humidity, which can lead to its deliquescence or transformation into other, more hydrated cobalt sulfates. Avoid acids, detergents, and high temperatures. ## Storage Specimens should be stored in a dry place, preferably in tightly sealed containers (e.g., "membrane boxes" or boxes with a desiccant). Display should be in a closed cabinet, away from sources of moisture and direct sunlight.