Gunningite
Chemical formula: Zn<sup>2+</sup>S<sup>6+</sup>O<sub>4</sub>·H<sub>2</sub>O
Gunningite is a rare, secondary zinc sulfate, occurring as white or colorless coatings and crusts.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.22
- Cleavage
- Good on {101}
- Fracture
- Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of gunningite is based on its characteristic occurrence as a secondary product in the oxidation zones of zinc deposits. Key features include its white color, low hardness, solubility in water, and co-occurrence with other sulfates. However, definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Gunningite can be confused with other white, secondary sulfates, such as goslarite (ZnSO₄·7H₂O) or bianchite (ZnSO₄·6H₂O). It differs from them in its degree of hydration, which translates into slightly different physical properties and crystallographic parameters. Goslarite often forms acicular crystals, while gunningite mainly occurs as crusts and coatings. ## Crystal Forms Gunningite crystals are very small, usually less than 1 mm in size. It crystallizes in the monoclinic system, forming fine-grained aggregates, crusts, and efflorescences on the surface of other minerals or rocks.
Geological environment
## Genesis Gunningite is a secondary mineral. It forms in the oxidation (weathering) zones of ore deposits, as a result of the slow oxidation of sphalerite (ZnS) under low humidity conditions. It is a typical mineral for dry or desert climates, where rainfall is unable to dissolve and leach it away. ## Mineral Associations It co-occurs with other minerals from the oxidation zone, such as sphalerite (as a primary mineral), goslarite, bianchite, epsomite, melanterite, gypsum, anglesite, and cerussite. ## Localities The most important, confirmed gunningite localities worldwide include the Keno Hill Mine in Yukon (Canada), from which the type material originates; the Comstock Mine in Nevada and the Superior Mine in Arizona (USA); as well as some mines in Germany (e.g., Rammelsberg) and Australia.
Rarity
Rare
For collectors
## Quality Criteria For collectors, specimens where gunningite forms rich, well-developed coatings or interesting speleothems are of the highest value. Samples where white or colorless coatings contrast with the color of the host rock are desirable. Due to the microscopic size of the crystals, their individual form is not the primary criterion for evaluation. ## Popular Localities Specimens from the type locality, the Keno Hill Mine in Yukon, are particularly prized by specialist collectors. Samples from classic localities in Arizona (USA) are also of interest.
Care and storage
## Cleaning Gunningite specimens are very sensitive to water, in which they readily dissolve. Mechanical cleaning is highly risky due to the mineral's fragility and softness. If absolutely necessary, a very soft brush can be used to remove loose dust. ## What to Avoid Contact with water and other liquids must be strictly avoided. The mineral is hygroscopic, meaning it absorbs moisture from the air, which can lead to its slow dissolution and destruction. It should be protected from high humidity, temperature changes, and direct sunlight. ## Storage Gunningite specimens require storage in dry, stable conditions. The best solution is to place them in tightly sealed containers (so-called "perky boxes") or display cases with a desiccant (e.g., silica gel).