Bieberite
Chemical formula: Co<sup>2+</sup>S<sup>6+</sup>O<sub>4</sub>·7H<sub>2</sub>O
Bieberite is a hydrated cobalt sulfate, forming characteristic pink-red, water-soluble coatings and efflorescences.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous
- Streak
- White
- Density
- 1.9
- Cleavage
- Perfect on {010}
- Fracture
- Conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification The most important diagnostic feature of bieberite is its intense pink-red color and complete solubility in water. This mineral has a characteristic, slightly bitter and astringent taste (taste testing is not recommended and dangerous). It occurs in a specific environment – as a weathering product in cobalt ore mines. ## Distinguishing from Similar Minerals Bieberite can be confused with erythrite (cobalt arsenate), which also has a pink or red color. However, erythrite is insoluble in water, crystallizes as acicular or bladed crystals, and is harder. Another similar mineral is sphaerocobaltite (cobalt carbonate), which is also pink, but has significantly greater hardness (approx. 4) and reacts with acids, without dissolving in water. ## Crystal Forms Well-formed bieberite crystals are extremely rare and appear as small, prismatic columns. It usually forms fibrous, acicular aggregates, and most often occurs as crusts, coatings, efflorescences, and small stalactites in mine workings.
Geological environment
## Genesis Bieberite is a secondary mineral. It forms in the oxidation (weathering) zone of ore deposits containing cobalt, such as cobaltite, skutterudite, or smaltite. It forms under dry conditions, as a product of dehydration of other sulfates or direct oxidation of sulfides in a water-poor environment. It is a typical mine mineral, currently forming on the walls of old adits and drifts. ## Mineral Associations This mineral co-occurs with other secondary cobalt and nickel minerals. It is most often accompanied by erythrite, annabergite, morenosite, gypsum, as well as the primary ore minerals from which it forms, such as cobaltite, skutterudite, or pyrite. ## Localities The most important localities worldwide include the historical site in Bieber (Hesse, Germany) and in the Schneeberg and Annaberg regions in Saxony (Germany). It also occurs in Jáchymov (Czech Republic), in mines in the Cobalt region in Ontario (Canada), and in several locations in the USA (e.g., Colorado and Idaho).
Rarity
Rare
For collectors
## Quality Criteria The most valued bieberite specimens are those that exhibit an intense, saturated pink-red color. Rare stalactitic forms or well-preserved, fluffy fibrous aggregates are exceptionally sought after. Due to the mineral's instability, well-protected specimens on attractive matrix rock command a higher value. Specimen size also matters, but even small samples with good color are attractive to collectors. ## Popular Localities Classic and most prized specimens come from historical German localities such as Bieber and Schneeberg. Currently, specimens from Bou Azzer in Morocco, known for its abundance of cobalt minerals, also appear on the market.
Care and storage
## Cleaning Bieberite must absolutely not be cleaned wet, as it completely dissolves in water. Specimens can only be cleaned mechanically, using a very soft brush to remove dust or compressed air from a safe distance. ## What to Avoid Avoid contact with water and any moisture, including very humid air. Storage in a dry environment is crucial, as in humid air the mineral can absorb water and deliquesce, and in overly dry air, it can lose its water of crystallization, fade, and disintegrate. It should be protected from all chemicals. ## Storage Bieberite specimens require special conditions. They are best stored in tightly sealed containers (e.g., "perky boxes") with the addition of a desiccant (silica gel). Display should only take place in enclosed, climate-controlled display cases, away from direct sunlight and heat sources.