Carlsonite

Chemical formula: (N³⁻H₄)₅Fe³⁺₃O(S⁶⁺O₄)₆·7H₂O

Carlsonite is a very rare, water-soluble iron ammonium sulfate, found as microscopic crystals in coal fire localities.

## Characteristics Carlsonite is a hydrated iron ammonium sulfate, occurring as very small, tabular or bladed crystals, which rarely exceed 50 micrometers in length. It typically forms aggregates, coatings, and efflorescences on rock surfaces. Due to the microscopic size of its crystals, its visual features are difficult to observe without specialized equipment. ## Physical Properties Carlsonite crystals exhibit a vitreous luster. This mineral is soft, with a Mohs hardness estimated at approximately 2. It is unstable and easily dissolves in water. ## Colors and Varieties Carlsonite ranges in color from pale yellow to yellow. No varieties have been distinguished. ## History and Name The mineral was named in honor of Ernest H. Carlson (born 1935), a retired professor of geology at Kent State University in Ohio, USA, in recognition of his contributions to mineralogy, including research on minerals from burning coal dumps. It was approved by the International Mineralogical Association (IMA) in 2015 (IMA2015-027), and its description was published in 2016. ## Uses Carlsonite has no industrial applications. It is solely an object of scientific and collector interest due to its rarity and specific formation environment.

Properties

Mohs hardness
2
Color
yellow to orange-brown
Luster
Vitreous
Streak
tan
Density
2.167
Cleavage
{001}
Fracture
Irregular/Uneven
Transparency
Transparent
Crystal system
Triclinic

Diagnostic features

## Identification Identification of carlsonite is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS), due to the microscopic size of the crystals. In the field, it can be suspected in specific environments (coal fires) based on its yellow color and co-occurrence with other sulfates. ## Distinguishing from Similar Minerals It can be confused with other secondary sulfates formed under similar conditions, such as boussingaultite, mascagnite, or clairite. Definitive differentiation from these minerals requires specialized laboratory analysis. ## Crystal Forms Carlsonite forms very small, tabular or bladed crystals, often grouped into rosette-like aggregates, spherulitic clusters, or thin coatings and efflorescences.

Geological environment

## Genesis Carlsonite is a secondary mineral, formed by sublimation from volcanic gases or gases released during fires in underground coal deposits or burning mine dumps. It crystallizes in lower temperature zones (below 150°C) from vapors rich in ammonia, sulfur oxides, and iron. ## Mineral Associations This mineral co-occurs with other sulfates and chlorides formed under similar conditions, such as boussingaultite, mascagnite, clairite, sal ammoniac, native sulfur, and hematite. ## Localities The only confirmed occurrence (type locality) is a burning coal dump near the village of Ravat in the Yagnob River valley, in the Zeravshan Mountains, Tajikistan.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to the microscopic nature of the mineral, its collector value is primarily scientific. The most desirable specimens are those where carlsonite forms rich, clearly visible aggregates under a microscope, and its identity has been analytically confirmed. Precise documentation of the locality is also crucial. ## Popular Localities The only source of carlsonite specimens is its type locality in Tajikistan. Material from this location is extremely rare on the collector's market.

Care and storage

## Cleaning Carlsonite specimens must not be cleaned wet, as the mineral is water-soluble. Dust should only be removed using a soft brush or a stream of compressed air from a safe distance. ## What to Avoid Contact with water, water vapor, and high humidity must be strictly avoided, as these can dissolve or damage the crystals. The mineral is unstable and sensitive to temperature changes. It should be protected from all chemicals. ## Storage Carlsonite specimens must be stored in dry conditions, preferably in sealed containers (e.g., "perky box" type) with a desiccant (silica gel). They should be kept at a stable temperature, away from direct sunlight.

External references

Sources

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