Therasiaite

Chemical formula: (N₃-H₄)₃KNa₂Fe₂+Fe₃+(S₆+O₄)₃Cl₅

Therasiaite is an extremely rare sulfate-chloride mineral of iron, potassium, sodium, and ammonium, forming microscopic crystals in volcanic exhalations.

## Characteristics Therasiaite is a complex sulfate and chloride containing ammonium, potassium, sodium, and iron in the +2 and +3 oxidation states. It occurs as very small, thin, tabular crystals with a hexagonal outline, rarely exceeding 0.2 mm in size. These crystals form aggregates, coatings, and thin crusts on volcanic rocks. The mineral is a product of volcanic gas sublimation in active fumaroles. ## Physical Properties Therasiaite crystals are transparent and exhibit a vitreous luster. Due to their microscopic size and rarity, physical properties such as hardness, density, or fracture have not yet been precisely determined. ## Colors and Varieties This mineral is characterized by a uniform, dark reddish-brown color. No color varieties or commercial forms are known. ## History and Name Therasiaite was officially described as a new mineral in 2014. Its name comes from the ancient Greek name of the island of Santorini - Therasia (Θηρασία), where its occurrence in fumarole products was also confirmed. Importantly, the type locality (locus typicus), the place of its first scientific description, is considered to be the "Arsenatnaya" fumarole on Tolbachik volcano in Kamchatka, Russia. ## Applications Due to its extreme rarity and microscopic size, therasiaite has no practical applications. It is solely an object of scientific interest and a valuable acquisition for specialized micromount mineral collectors.

Properties

Luster: Vitreous
Transparency: Transparent
Crystal system: Trigonal

Diagnostic features

## Identification Identifying therasiaite in collector conditions is very difficult and relies mainly on the geological context. A key indicator is its occurrence in products of active, high-temperature volcanic fumaroles. The dark reddish-brown color and the form of thin, tabular crystals with a hexagonal outline are characteristic features. However, definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS). ## Distinguishing from Similar Minerals Therasiaite can be confused with other darkly colored volcanic sublimation products, such as fine-grained hematite or other complex sulfates. Differentiation based on visual characteristics is practically impossible. Analysis of associated minerals may be helpful, but only laboratory tests provide a definitive determination. ## Crystal Forms The mineral forms very thin, tabular crystals with a hexagonal outline. These crystals often arrange into rosette-like aggregates, fan-shaped clusters, or form thin crusts and coatings on the surface of volcanic rocks.

Geological environment

## Genesis Therasiaite is a fumarolic mineral. It forms through direct sublimation from hot volcanic gases (exhalations) at temperatures of approximately 450-500°C. It crystallizes on the walls of fumarole channels, reacting with the surrounding volcanic rocks. ## Mineral Associations This mineral occurs in association with other rare fumarolic minerals. The most common associations include adranosite-(Fe), adranosite, alunite, hematite, kremersite, letovicite, and sylvine. ## Localities Only two confirmed occurrences of therasiaite are known worldwide. The first is the type locality – the "Arsenatnaya" fumarole on the second cinder cone of Tolbachik volcano (Kamchatka, Russia). The second is the historical locality from which the mineral took its name – fumaroles on Therasia island (Santorini) in Greece.

Rarity

Extremely rare

For collectors

## Quality Criteria Therasiaite is a mineral almost exclusively for "micromount" collections. The value of a specimen is primarily determined by the quality and size of the microcrystals. Specimens with well-formed, sharp, undamaged tabular crystals are most prized. Rich aggregates forming striking clusters and aesthetic associations with other rare fumarolic minerals, especially if they contrast in color, are also highly valued. ## Popular Localities Both known localities – Tolbachik volcano in Kamchatka and Therasia island in Greece – provide material of scientific importance. However, Tolbachik is the source of the best-formed and most commonly found (on a micro scale) therasiaite specimens, as well as many other unique fumarolic minerals, making it more renowned among specialized collectors.

Care and storage

## Cleaning Therasiaite specimens are extremely delicate and potentially water-soluble. They must absolutely not be cleaned with water, steam, or any chemical liquids. The only safe method for dust removal is very gentle blowing with compressed air from a safe distance or using a soft brush. ## What to Avoid Avoid contact with water and moisture, which can dissolve or damage the crystals. The mineral is thermally unstable – as a sublimation product, it can decompose under high temperatures. Protect it from all chemicals, ultrasound, and direct, strong light. ## Storage Specimens should be stored in a dry place, preferably in tightly sealed "micromount" boxes, which protect against dust, moisture, and mechanical damage. Storage at a stable room temperature is crucial for maintaining the mineral's integrity.

Sources

IMA Mineral List (CNMNC)