Thermessaite-(NH_4_)

Chemical formula: (N₃-H₄)₂AlF₃(S₆+O₄)

An extremely rare ammonium sulfatofluoride-aluminate, discovered as a product of fumarolic activity on the Thíra volcano in Greece.

## Characteristics Thermessaite-(NH₄) is a mineral with a unique chemical composition, belonging to the group of ammonium sulfatofluoride-aluminates. It forms very fine, colorless crystals with a tabular or lamellar habit, reaching up to 200 micrometers in size. It is observed as aggregates and coatings on volcanic rocks. Due to its extreme rarity and small crystal size, its visual characteristics are difficult to assess without specialized equipment. ## Physical Properties The crystals exhibit a vitreous luster. The mineral is transparent. Hardness and density have not been precisely measured due to the small amount of available material. ## History and Name The mineral's name comes from the ancient name of the island of Thíra (Santorini) in Greece - "Thermessa," meaning "hot." This refers to its genesis in hot volcanic exhalations (fumaroles). The suffix -(NH₄) specifies the presence of the ammonium ion as the dominant cation. The mineral was officially approved by the International Mineralogical Association (IMA) in 2023 (IMA2023-090). The discovery was made by an international team of researchers analyzing volcanic gas sublimation products. ## Applications Thermessaite-(NH₄) has no commercial or industrial applications. Its significance is purely scientific and collectible, as a unique product of natural volcanic processes.

Properties

Luster: Vitreous
Streak: White
Transparency: Transparent
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of this mineral is impossible without advanced laboratory techniques, such as X-ray diffraction (XRD) and chemical spectroscopy (EDS/WDS). It is unrecognizable in field and collecting conditions. It occurs as fine, colorless, tabular crystals in fumarole products. ## Distinguishing from Similar Minerals It can be confused with other volcanic sublimation products, such as sal ammoniac (ammonium chloride) or other sulfates. Differentiation requires specialized chemical and crystallographic analysis. Crucial is the confirmation of the simultaneous presence of ammonium ions, aluminum, fluorine, and the sulfate group. ## Crystal Forms It forms very small, tabular or lamellar crystals, often grouped into irregular aggregates, rosettes, or forming thin coatings and crusts.

Geological environment

## Genesis Thermessaite-(NH₄) is a mineral of volcanic origin. It forms as a result of direct sublimation (resublimation) of hot gases (fumaroles) at temperatures of approximately 150-200°C. It crystallizes on the surface of volcanic rocks near active exhalations, where gases rich in ammonium, fluorine, sulfur, and aluminum compounds react and deposit in solid form. ## Mineral Associations This mineral co-occurs with other volcanic sublimation products. In the type locality, its presence has been noted alongside anhydrite (CaSO₄), sal ammoniac (NH₄Cl), and the newly discovered mineral thirasiaite. ## Localities The only confirmed occurrence worldwide is the type locality - active fumaroles in the Nea Kameni crater on the Thíra volcano (Santorini), in the Cyclades archipelago, Greece.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its extreme rarity, every analytically confirmed specimen is extremely valuable to specialized systematic and micromount mineral collectors. Most highly valued are specimens where crystals are well-formed, create rich aggregates, and are clearly visible on the rock matrix. The presence of associated minerals, especially other rare sublimation products, also increases scientific and collectible value. ## Popular Localities The only source of specimens is the Nea Kameni crater on the Greek island of Thíra (Santorini). Material acquisition from this site is strictly controlled and requires specialized scientific expeditions.

Care and storage

## Cleaning Specimens of this mineral are extremely delicate and potentially water-soluble. They should absolutely not be cleaned wet. Any contaminants can only be removed very carefully using compressed air (from a safe distance) or tweezers under a microscope. ## What to Avoid Avoid contact with water, water vapor, and any chemicals. The mineral is sensitive to moisture and temperature changes. It should not be heated or exposed to direct sunlight. Vibrations and shocks can damage the delicate crystals. ## Storage Specimens must be stored in sealed, dry containers, preferably with a desiccant (e.g., silica gel). Specialized "micromount" boxes are recommended to protect against mechanical damage and dust. Display should be under controlled conditions.