Dorallcharite

Chemical formula: Tl₁+Fe₃+₃(S₆+O₄)₂(OH)₆

An extremely rare thallium iron sulfate from the alunite supergroup, forming microscopic, yellowish-brown crystals.

## Characteristics Dorallcharite is a very rare mineral from the alunite supergroup, being a hydrated thallium iron sulfate. It occurs as earthy, powdery, or compact coatings and crusts. Its color is usually yellowish-brown. Individual crystals are microscopic in size, making them rarely visible to the naked eye. Due to its chemical composition, it is a mineral of primarily scientific importance. ## Physical Properties Dorallcharite crystals, visible only under high magnification, exhibit a dull luster and are translucent. The Mohs hardness is estimated at approximately 3. The density calculated based on the chemical formula and unit cell parameters is 3.81 g/cm³. ## Colors and Varieties This mineral is monochromatic – it occurs exclusively in yellowish-brown shades. No color varieties or commercial varieties are known. ## History and Name The name dorallcharite comes from its discovery location. The first part, “Dor”, refers to the nearby village of Dolno Rožden, while the second, “Allchar”, is the name of the deposit where it was found. The mineral was approved by the International Mineralogical Association (IMA) in 1992. ## Applications Due to its extreme rarity and the toxic nature of thallium, dorallcharite has no commercial or industrial applications. It serves solely as an object of scientific research and interest for specialized collectors of microminerals.

Properties

Mohs hardness: 3
Luster: Dull
Streak: Pale yellow
Density: 3.81
Cleavage: Distinct on {0001}
Transparency: Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of dorallcharite is impossible based on visual characteristics alone. Its appearance (yellowish-brown, earthy coatings) is non-specific and can resemble many other secondary iron minerals. Definitive identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS) to confirm its unique chemical composition (presence of thallium, iron, and sulfur) and X-ray diffraction (XRD) to verify the crystal structure. ## Distinguishing from Similar Minerals Dorallcharite can be confused with other minerals from the jarosite group, such as jarosite (KFe₃(SO₄)₂(OH)₆), natrojarosite (NaFe₃(SO₄)₂(OH)₆), or hydroniumjarosite ((H₃O)Fe₃(SO₄)₂(OH)₆). All have similar appearance and physical properties. Distinguishing them from each other is only possible through chemical analysis. It can also be confused with other secondary iron sulfates and arsenates, e.g., goethite or scorodite in their earthy varieties. ## Crystal Forms It most often forms earthy, powdery, or compact aggregates and crusts. Less frequently, very fine, platy or rhombohedral crystals are observed, whose size does not exceed several tens of micrometers.

Geological environment

## Genesis Dorallcharite is a secondary mineral, forming in the oxidation (weathering) zone of low-temperature, polymetallic hydrothermal deposits. Its formation is associated with the weathering processes of primary sulfides and sulfosalts rich in thallium, arsenic, and antimony in an acidic and strongly oxidizing environment. ## Mineral Associations This mineral occurs in association with other, often rare, thallium, arsenic, and antimony minerals. In the type locality, its co-occurrence with lorandite, realgar, orpiment, fangite, raguinite, marcasite, and pyrite has been noted. ## Localities The only confirmed occurrence of dorallcharite in the world is its type locality – the Allchar deposit, near Kavadarci in North Macedonia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of dorallcharite specimens, which are almost exclusively micromounts, is assessed based on the richness of the coating on the rock matrix and the aesthetics of the association with other rare minerals, especially crystalline lorandite, realgar, or orpiment. Individual crystals are too small to assess their form or purity without the use of a scanning electron microscope. Collectible specimens are extremely difficult to obtain and are mainly found in institutional and systematic collections. ## Popular Localities The only source of specimens is the Allchar deposit in North Macedonia. The mineral is not commercially exploited, and access to the site is restricted.

Care and storage

## Cleaning **The mineral is highly toxic – direct contact should be avoided.** Cleaning specimens is not recommended and should be kept to an absolute minimum. All procedures should be performed with gloves. To remove dust, a soft brush can be used, or dust can be carefully blown off with compressed air from a safe distance. Absolutely avoid wet cleaning, using water or any chemicals. ## What to Avoid - **Skin contact:** Thallium is a highly poisonous element, absorbed through the skin. Hands should be thoroughly washed after any potential contact. - **Inhaling dust:** Any activities that could lead to dusting (e.g., scratching, crushing) should be avoided. - **Water and moisture:** As a sulfate, it may be sensitive to water. - **Acids and other chemicals:** They can easily destroy the mineral. ## Storage Dorallcharite specimens must be stored in tightly sealed, clearly labeled containers (e.g., “perky box” type) with a warning label about toxicity. They should be kept away from children, pets, and separate from other minerals in the collection to avoid accidental contamination.

Sources

IMA Mineral List (CNMNC)