D'ansite-(Fe)

Chemical formula: Na₂₁Fe₂+(S₆+O₄)₁₀Cl₃

A very rare, hygroscopic sodium and iron sulfate from the d'ansite group, discovered in the Kłodawa salt mine.

## Characteristics D'ansite-(Fe) is a mineral from the d'ansite group, which is a hydrated sodium and iron sulfate with chlorine. It most often forms well-developed, isometric crystals with an octahedral or rhombic dodecahedral habit, reaching several millimeters in size. It is colorless or takes on a pale greenish hue. It is characterized by a strong, vitreous luster. Its most characteristic feature is its high hygroscopicity – it absorbs moisture from the air, which can lead to its disintegration. ## Physical Properties This mineral is relatively soft, with a hardness of about 3 on the Mohs scale. It is transparent and brittle, with a conchoidal fracture. Its density is approximately 2.66 g/cm³. The most important physical property of d'ansite-(Fe) is its instability in a humid environment. It readily dissolves in water and absorbs water vapor from the surroundings, which requires special storage conditions. ## Colors and Varieties Typical specimens are colorless, less often pale greenish. No color or commercial varieties are distinguished. ## History and Name The mineral's name refers to the German chemist Jean D'Ans (1881-1969), who studied phase equilibria in salt deposits. The suffix -(Fe) indicates the dominance of iron (Latin: *ferrum*) in its chemical composition. The mineral was officially approved by the IMA in 2011, and its type locality is the "Kłodawa" Salt Mine in Poland. ## Applications D'ansite-(Fe) has no industrial application. It is solely an object of scientific and collecting interest as a rare and specific component of evaporite deposits.

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: White
Density: 2.66
Cleavage: None
Fracture: Conchoidal
Transparency: Transparent
Crystal system: Isometric

Diagnostic features

## Identification Key diagnostic features of d'ansite-(Fe) are its isometric, well-formed crystals (octahedra, rhombic dodecahedra), vitreous luster, and occurrence in a saline evaporite environment. Its extreme hygroscopicity and easy solubility in water are the most important confirming tests, although they are destructive in nature. ## Distinguishing from Similar Minerals It can be confused with other colorless salt minerals, such as halite. However, halite has excellent, three-directional cleavage (cubic), which d'ansite-(Fe) does not exhibit. Distinguishing it from other minerals of the d'ansite group (e.g., d'ansite-(Mn) or d'ansite-(Mg)) is practically only possible through chemical analysis. ## Crystal Forms It forms single, overgrown crystals with an isometric habit. Octahedral {111} and rhombic dodecahedral {110} forms dominate, often occurring in combination. Crystals are usually well-formed, with sharp edges and smooth faces.

Geological environment

## Genesis D'ansite-(Fe) is an evaporite mineral. It forms in the final stages of salt crystallization in marine basins, under conditions of high salinity and specific chemical composition of brines. It forms as a result of diagenetic or metamorphic processes occurring within salt domes, where iron-rich brine is trapped. ## Mineral Associations This mineral coexists with other salts forming evaporites. Its most common associated minerals are halite, polyhalite, anhydrite, leonite, blödite, kainite, and langbeinite. ## Localities The most important and best-documented occurrence in the world, and also the type locality, is the "Kłodawa" Salt Mine near Kłodawa, in the Greater Poland Voivodeship, Poland. It has also been reported in salt deposits in Thuringia, Germany.

Rarity

Very rare

For collectors

## Quality Criteria As a typically specialized mineral, its collector value primarily depends on the quality and form of the crystals. Sharp, well-formed, transparent crystals with a distinct luster are most highly prized. Their size and placement on the rock matrix are also very important, especially in aesthetic contrast with associated minerals (e.g., on colorful halite). Specimens of intergrowths or combinations of different crystallographic forms are also sought after. ## Popular Localities The only source of specimens of collector significance is the type locality – the "Kłodawa" Salt Mine in Poland. Specimens from this location are the standard for this mineral and the most desired by collectors of rare minerals.

Care and storage

## Cleaning D'ansite-(Fe) specimens are extremely sensitive to moisture and water. Absolutely no liquids should be used for cleaning. The only safe method for dust removal is to use a soft, completely dry brush or carefully use compressed air from a safe distance. ## What to Avoid Contact with water, water vapor, and humid air must be strictly avoided. The mineral is highly hygroscopic and will be destroyed (dissolved) upon contact with moisture. It should be protected from sudden temperature changes, which can cause water vapor condensation. ## Storage Storage requires completely dry conditions. The best solution is to place the specimen in a sealed, airtight container (e.g., a "perky box") along with a moisture-absorbing agent, such as silica gel. Display should only take place in enclosed display cases with controlled humidity.

Sources

IMA Mineral List (CNMNC)