Poitevinite
Chemical formula: Cu<sup>2+</sup>S<sup>6+</sup>O<sub>4</sub>·H<sub>2</sub>O
Poitevinite is a rare, secondary copper sulfate, forming tiny, pink crystals and efflorescences, closely related to chalcanthite.
Properties
- Mohs hardness
- 3.5
- Luster
- Vitreous
- Streak
- Pale pink
- Density
- 3.26
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Poitevinite can be identified by its characteristic pinkish-violet color, occurrence as small, prismatic crystals, and its sensitivity to water. It often forms efflorescences and crusts on sulfide rocks. ## Distinguishing from Similar Minerals Poitevinite can be confused with other secondary copper sulfates. It is distinguished from chalcanthite (CuSO₄·5H₂O) by its pinkish, rather than blue, color. From bonattite (CuSO₄·3H₂O), it is practically impossible to distinguish without advanced studies (e.g., X-ray diffraction), as they have very similar appearance and properties. It also differs from them in its crystallographic system. ## Crystal Forms Crystals are usually very small, with a short prismatic habit. It most often forms granular aggregates, crusts, efflorescences, and rosette-like clusters.
Geological environment
## Genesis Poitevinite is a secondary mineral, formed in the oxidation (weathering) zones of copper sulfide deposits. It forms under dry conditions, often as a result of dehydration of more hydrated copper sulfates, such as chalcanthite, in a low-humidity environment, for example, in mines. ## Mineral Associations It most often co-occurs with other secondary copper sulfates, such as chalcanthite, bonattite, and also with the sulfides from which it originates, e.g., chalcopyrite and bornite. Gypsum may also accompany it. ## Localities The most important and classic locality, from which the type material originates, is the Centennial Mine in Calumet, Houghton County, Michigan, USA. This mineral has also been identified in several other locations worldwide, including mines in the Atacama region of Chile and the Kipushi Mine in the Democratic Republic of Congo.
Rarity
Very rare
For collectors
## Quality Criteria The most valuable poitevinite specimens are those that have well-formed, visible to the naked eye crystals of intense, pinkish-violet color. Due to the microscopic size of the crystals, specimens with distinct, larger aggregates are particularly prized. The aesthetics of the host rock on which the mineral grows is also important. ## Popular Localities Specimens from the type locality – the Centennial Mine in Michigan, USA – are by far the most sought after by collectors. They are historically most important and serve as a reference point for this mineral.
Care and storage
## Cleaning Poitevinite specimens are very sensitive to water and moisture. They should not be washed with water or any liquids. To remove dust, a very soft brush or compressed air from a safe distance can be used very carefully. ## What to Avoid Avoid contact with water, which can dissolve the mineral or cause its transformation into chalcanthite. High air humidity, which leads to its slow degradation, should be avoided. The mineral is sensitive to temperature changes and should not be exposed to direct sunlight. ## Storage Poitevinite requires storage in dry conditions. It is best kept in a sealed, closed collector's box (a "perky box") or in a display case with a desiccant (e.g., silica gel). Display should take place in a controlled environment, away from heat and light sources.