Möhnite

Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)K<sub>2</sub>Na(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>

Möhnite is a rare, water-soluble sulfate, forming colorless, tabular crystals, discovered in volcanic fumarole deposits.

## Characteristics Möhnite is a hydrated ammonium, potassium, and sodium sulfate. This mineral forms very small, colorless, tabular or platy crystals, usually not exceeding 0.2 mm in length. It occurs as single crystals or small aggregates. Due to its water solubility, it is an unstable mineral in a humid environment. ## Physical Properties Möhnite crystals exhibit a vitreous luster. They are transparent and colorless. Hardness and density have not been precisely determined due to the small size and fragility of the crystals. ## Colors and Varieties This mineral is colorless. No varieties have been distinguished. ## History and Name The mineral's name honors Gerhard Möhn (born 1959), a German chemist and mineral collector, specializing in minerals from Mount Vesuvius and the Eifel volcanic complex. Möhnite was approved as a new mineral by the International Mineralogical Association (IMA) in 2017 (IMA2017-051). It was described by Nikita V. Chukanov and his colleagues. ## Uses Möhnite has no industrial application. It is solely an object of scientific and collecting interest due to its rarity and specific formation conditions.

Properties

Luster
Vitreous
Streak
White
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Amateur identification of möhnite is practically impossible. It requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD), due to the microscopic size of the crystals and similarity to other sulfates of the arcanite group. ## Distinguishing from Similar Minerals It can be confused with other colorless, soluble sulfates found in fumarolic environments, such as arcanite (K₂SO₄) or thenardite (Na₂SO₄). Certain differentiation is only possible based on chemical composition analysis. ## Crystal Forms Möhnite crystallizes as very small, thin, tabular or platy crystals, often with a hexagonal outline.

Geological environment

## Genesis Möhnite is a mineral of volcanic origin, formed by the sublimation of volcanic gases in a fumarolic environment. It crystallizes directly from hot gases (200-250°C) rich in sulfur, ammonia, potassium, and sodium, which deposit on crater walls or nearby. ## Mineral Associations It co-occurs with other fumarolic minerals, such as kremersite, sal ammoniac, thenardite, and native sulfur. ## Localities The only confirmed occurrence (type locality) is an active fumarole in the La Fossa crater on Vulcano Island, part of the Aeolian Islands archipelago in Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a möhnite specimen primarily depends on the presence of well-formed, identifiable crystals, even if they are microscopic in size. The most prized are rich crystal aggregates on a contrasting matrix. Due to its extreme rarity, any analytically confirmed specimen is valuable for specialized collectors. ## Popular Localities The only source of specimens is the type locality – the fumaroles of the La Fossa crater on Vulcano Island, Italy.

Care and storage

## Cleaning The mineral is water-soluble, therefore it must absolutely not be cleaned wet. Mechanical cleaning is inadvisable due to the extreme fragility and small size of the crystals. It is safest to leave the specimen in its original state. ## What to Avoid Avoid contact with water, water vapor, and high humidity, which can dissolve or damage the crystals. Also avoid all chemicals, ultrasonics, and sudden temperature changes. ## Storage Möhnite specimens must be stored in a dry environment. It is recommended to keep them in tightly sealed containers (so-called "perky boxes") or display cases with a desiccant (e.g., silica gel) to protect them from atmospheric moisture.

Sources

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