Lausenite

Chemical formula: Fe<sup>3+</sup><sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>3</sub>·5H<sub>2</sub>O

Lausenite is a rare, water-soluble iron(III) sulfate, occurring as a weathering product of pyrite or marcasite.

## Characteristics Lausenite is a secondary mineral that forms as a result of the oxidation of iron sulfides, such as pyrite and marcasite, under low humidity conditions. It occurs as fibrous or capillary aggregates, as well as coatings and efflorescences on host rocks. Due to its water solubility, it is an unstable mineral in humid environments and rarely preserved in natural conditions, being most commonly found in dry mines or on mine dumps. ## Physical Properties This mineral is characterized by a silky luster. It is very soft, with a Mohs hardness of approximately 1.5. It is also very light, with a density close to 2.1 g/cm³. Its most characteristic feature is its water solubility. ## Colors and Varieties Lausenite typically ranges in color from white to yellowish to brownish. The coloration depends on the degree of hydration and the presence of impurities. ## History and Name The mineral was first described by Czech mineralogist Bohuslav Ježek in 1926. The name honors Carl Lausen, a mining engineer from the United Verde Mine in Jerome, Arizona (USA), where the mineral was discovered. Initially, it was described as a sulfate with the formula Fe₂(SO₄)₃·6H₂O, but later studies showed that natural lausenite actually has 5 molecules of water (formula Fe₂(SO₄)₃·5H₂O), and the hexahydrate is a synthetic substance.

Properties

Mohs hardness
1.5
Luster
Silky
Streak
White to yellowish
Density
2.06-2.11
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification The key diagnostic feature of lausenite is its complete solubility in water. Its fibrous or capillary appearance, silky luster, and occurrence as efflorescences on iron sulfides in dry environments (e.g., old mines) are also very characteristic. ## Distinguishing from Similar Minerals Lausenite can be confused with other secondary iron sulfates, such as kornelite, coquimbite, or rhomboclase. Kornelite (Fe₂(SO₄)₃·7H₂O) is very similar but contains more crystallization water. Coquimbite (Fe₂(SO₄)₃·9H₂O) usually forms more distinct, tabular or pyramidal crystals. Rhomboclase (HFe(SO₄)₂·4H₂O) is also water-soluble but has a different chemical composition. A definitive distinction between these minerals often requires chemical analysis (XRD). ## Crystal Forms Lausenite forms very fine, acicular or capillary crystals, which usually occur as tangled aggregates, coatings, and crusts.

Geological environment

## Genesis Lausenite is a secondary mineral, formed as a result of the weathering (oxidation) of iron sulfide minerals, mainly pyrite (FeS₂) and marcasite (FeS₂). It forms in the oxidation zones of ore deposits, in dry and well-ventilated mine workings, on mine dumps, and as a product of mine fires (so-called post-mining mineral). Its formation is limited to environments with very low humidity. ## Mineral Associations This mineral co-occurs with other iron sulfates, such as kornelite, coquimbite, rhomboclase, voltaite, as well as native sulfur, pyrite, and marcasite. ## Localities The most important lausenite localities worldwide include the United Verde Mine in Jerome, Arizona, USA (type locality); Rammelsberg in the Harz Mountains, Germany; Calamita on Elba Island, Italy; and also the burning shale dumps in Wrexham County, Wales, Great Britain.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of lausenite is specific and stems mainly from its rarity and its well-defined "post-mining mineral" character. The most prized specimens are rich, "fluffy" aggregates of fine, capillary crystals covering a significant area of the host rock. Purity (lack of dirt) and intensity of color (from white to yellowish) also increase the value of the specimen. Due to its delicacy, the state of preservation is crucial – undamaged specimens, without signs of dissolution, are much more highly valued. ## Popular Localities Specimens from the type locality, the United Verde Mine in Arizona, have particular historical value. High-quality, rich aggregates also come from Rammelsberg in Germany.

Care and storage

## Cleaning Lausenite is extremely sensitive to water and dissolves in it. **It must absolutely not be cleaned wet.** The only safe method is to use a very soft, dry brush to remove dust or use compressed air from a safe distance. ## What to Avoid Avoid all contact with water, water vapor, and high air humidity, which can cause the mineral to dissolve or chemically alter. Also avoid ultrasonics and all chemicals. It is a very brittle and delicate mineral, sensitive to mechanical damage. ## Storage Lausenite specimens must be stored in controlled, low-humidity conditions. The best solution is a sealed container (a "perky box") with a desiccant (e.g., silica gel). It should be protected from dust and mechanical damage, preferably in a separate, padded box.

Sources

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