Tschermigite
Chemical formula: N<sup>3-</sup>H<sub>4</sub>Al(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·12H<sub>2</sub>O
Tschermigite is a hydrated ammonium aluminum sulfate, occurring as fibrous or crust-like coatings and efflorescences.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous, Silky
- Streak
- White
- Density
- 1.64 - 1.65
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Cubic
Diagnostic features
## Identification Characteristic features of tschermigite include its occurrence as fibrous efflorescences and coatings, low hardness, vitreous or silky luster, and solubility in water. It often has a sweet-astringent taste, but taste testing is strongly discouraged due to potential contaminants. ## Distinguishing from Similar Minerals Tschermigite can be confused with other secondary sulfates and alums, such as potassium alum, halotrichite, or epsomite. Differentiation often requires chemical analysis (test for the presence of ammonium ion). Unlike gypsum, tschermigite is much softer and soluble in water. ## Crystal Forms Well-formed crystals are rare and take the form of octahedra typical of minerals from the alum group. Much more often, it forms fibrous, radial, botryoidal aggregates, as well as crusts, coatings, and small stalactites.
Geological environment
## Genesis Tschermigite is a secondary mineral, forming under specific conditions. It forms as a sublimation product from coal and bituminous shale dump fires, where escaping ammonia reacts with sulfates produced from pyrite oxidation. It also forms in volcanic exhalation zones (fumaroles) and as a product of guano decomposition in arid climates. ## Mineral Associations It co-occurs with other minerals formed under similar conditions, such as native sulfur, sal ammoniac, mascagnite, alunogen, gypsum, potassium alum, and realgar and orpiment in fumarole deposits. ## Localities Key localities worldwide include Čermníky in the Czech Republic (type locality), mine dumps in the Ruhr Area (Germany), the vicinity of Delle, Scandale, and Naples (Vesuvius) in Italy. It also occurs in the Alum Cave mine in Tennessee and at The Geysers in California (USA).
Rarity
Rare
For collectors
## Quality Criteria The most prized by collectors are well-formed, transparent octahedral crystals, which are, however, extremely rare. Rich, fibrous aggregates with a silky luster, covering a significant area of the matrix rock, are also highly valued. Purity (absence of impurities and inclusions) and lack of mechanical damage are crucial, as is a precisely determined origin locality. ## Popular Localities Specimens from classic, historical localities, such as Čermníky in the Czech Republic or the vicinity of Vesuvius in Italy, are particularly esteemed. Visually attractive, fibrous aggregates also come from burning dumps in Germany and from some localities in the USA.
Care and storage
## Cleaning Tschermigite specimens are extremely sensitive to water, in which they easily dissolve. Wet cleaning is absolutely forbidden. Only very careful dust removal with a soft brush or a stream of compressed air from a distance is permissible. ## What to Avoid Contact with water and any moisture, which leads to the dissolution of the mineral, must be strictly avoided. Specimens are hygroscopic, meaning they absorb moisture from the air, so they must not be stored in damp rooms. They should be protected from high temperatures, which can cause the loss of crystallization water and damage the specimen. ## Storage Storage requires ensuring dry conditions. The best solution is to place the specimen in a sealed, airtight container (e.g., a "membrane box" or a box with a gasket) along with a desiccant (e.g., silica gel). Avoid exposure to direct sunlight.