Fleisstalite

Chemical formula: Fe₂+(S₄+O₃)·₃H₂O

Fleisstalite is a very rare, hydrated iron(II) sulfite, forming small, colorless to pale green, bladed crystals.

## Characteristics Fleisstalite is a mineral from the sulfite group, chemically a hydrated iron(II) sulfite. It occurs as very small, bladed or acicular crystals, rarely exceeding 1 mm in length. The crystals are usually colorless, white, or acquire a pale green tint due to partial oxidation of iron. They form small, radial aggregates or are dispersed on the surface of the host rock. Due to its size and rarity, it is a mineral of interest mainly to specialized collectors and scientists. ## Physical Properties Fleisstalite crystals exhibit a vitreous luster. The hardness of the mineral has not been precisely determined, but it is very soft and brittle. It is transparent to translucent. The density calculated from the formula and unit cell parameters is approximately 2.26 g/cm³. ## History and Name The mineral was discovered in the Fleißtal valley, in the Goldberg mountain group in the Hohe Tauern (Carinthia, Austria). Its name, approved by the International Mineralogical Association (IMA) in 1998, comes directly from its discovery location (type locality). It was described by a team of scientists, including G. Niedermayr and W. Postl.

Properties

Luster: Vitreous
Streak: White
Density: 2.26
Cleavage: Perfect on {010}
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of fleisstalite under amateur conditions is practically impossible. It requires advanced analytical methods, such as X-ray diffraction (XRD) or Raman spectroscopy. Preliminary suspicion can be drawn based on the occurrence location (mine dumps in the Fleißtal valley), crystal habit (small, acicular or bladed), and instability upon contact with moisture. ## Distinguishing from Similar Minerals It can be confused with other secondary sulfites or iron sulfates, such as rozenite or melanterite, which also form white or greenish coatings and efflorescences. Fleisstalite is distinguished from them by its unique crystal structure and chemical composition, which can only be determined in a laboratory. ## Crystal Forms Fleisstalite crystals are very small, with a bladed or acicular habit. They typically form small, radial or chaotically arranged aggregates on rock surfaces.

Geological environment

## Genesis Fleisstalite is a secondary mineral, formed as a result of the weathering of sulfide minerals, mainly pyrite (FeS₂), under specific anaerobic conditions or with limited oxygen access. It forms as an intermediate product in sulfide oxidation reactions. Its occurrence is limited to the microclimate prevailing in the dumps of former gold mines. ## Mineral Associations At the type locality, fleisstalite coexists with pyrite, quartz, and other rare secondary minerals such as kaatialaite (iron arsenate) and haidingerite (calcium arsenate). ## Localities The only confirmed and described occurrence of fleisstalite in the world is its type locality – historical mine dumps in the Fleißtal valley, in the Goldberg region, Carinthia, Austria.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to the extreme rarity and microscopic size of the crystals, every fleisstalite specimen is valuable from a scientific point of view. For collectors specializing in rare or systematic minerals, any specimen with analytically confirmed presence of the mineral will be valuable. The most desirable specimens are those with visible crystalline aggregates, even under high magnification, on a fragment of the host rock.

Care and storage

## Cleaning Fleisstalite specimens are extremely delicate and sensitive. Any mechanical cleaning and contact with water should be avoided. If cleaning is absolutely necessary, a stream of compressed air can be used very carefully from a safe distance to remove loose dust. ## What to Avoid Fleisstalite is unstable under atmospheric conditions. Contact with water, moisture, and high temperatures must be absolutely avoided. Under the influence of atmospheric oxygen and moisture, it easily oxidizes and decomposes, likely into iron sulfates (e.g., melanterite). It should not be exposed to direct sunlight. ## Storage Specimens should be stored in sealed, dry containers, preferably with a desiccant (e.g., silica gel). Storage in stable conditions, in a dark and dry place, is crucial for preserving the mineral's integrity.

Sources

IMA Mineral List (CNMNC)