Zinkosite
Chemical formula: Zn<sup>2+</sup>S<sup>6+</sup>O<sub>4</sub>
Zincosite is a synthetic, water-soluble zinc sulfate that occurs extremely rarely in nature as fine efflorescences.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.54
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification The key diagnostic feature of zincosite is its complete solubility in water. It occurs as white, soft, and brittle coatings or efflorescences in dry environments, most commonly in old mines. Reaction to water is the simplest and definitive test, though it destroys the sample. ## Distinguishing from Similar Minerals Zincosite can be confused with other white, secondary sulfates, such as goslarite (ZnSO₄·7H₂O) or epsomite (MgSO₄·7H₂O). Goslarite is a hydrated form of zinc sulfate and often forms acicular crystals or crusts. Distinguishing anhydrous zincosite from these minerals in field conditions is difficult and usually requires laboratory analysis (XRD), but zincosite is much rarer. ## Crystal Forms Zincosite crystals are extremely rare and microscopic in size. It usually forms earthy aggregates, powdery coatings, crusts, and efflorescences on other minerals or rocks.
Geological environment
## Genesis Zincosite is a secondary mineral, formed by the oxidation of sulfidic zinc ores, mainly sphalerite (ZnS), under very low humidity conditions. It forms as a dehydration product of other hydrated zinc sulfates, such as goslarite. Its occurrence is limited to dry, sheltered places, e.g., in old, inactive mine workings. ## Mineral Associations It most often co-occurs with minerals from which it forms or which accompany it in the oxidation zone. These are primarily sphalerite, goslarite, melanterite, epsomite, chalcanthite, and gypsum. ## Localities Confirmed, though extremely rare, occurrences of zincosite have been reported at the historical type locality in the Silber-Berg mine in Bodenmais, Bavaria (Germany), and in the San José mine in the Oruro department (Bolivia).
Rarity
Extremely rare
For collectors
## Quality Criteria Due to its extreme rarity, every analytically confirmed zincosite specimen has high scientific and collector value. The most desirable specimens are those where zincosite forms visible, even small, aggregates on the host rock, in association with other minerals. The purity and abundance of the coating increase the specimen's value. Due to the nature of the mineral, aesthetics are of secondary importance compared to its documentary value. ## Popular Localities The only source of collector-grade specimens is essentially the San José mine in Bolivia, from which a few samples have entered the market.
Care and storage
## Cleaning Zincosite must not be cleaned with water. Any contact with water, even a damp cloth, will cause it to dissolve and be destroyed. Only very careful removal of dust with a soft, dry brush or a stream of compressed air from a distance is permissible. ## What to Avoid Water, moisture, water vapor, and all chemicals must be absolutely avoided. The mineral is hygroscopic, meaning it absorbs moisture from the air, so storing it in a dry environment is crucial. Temperature changes, which can cause water vapor condensation, should also be avoided. ## Storage Zincosite specimens require specialized storage conditions. It is best to place them in a sealed, transparent container (a "perky box") along with a desiccant, such as silica gel. The container should be stored at a stable temperature, away from direct sunlight.