Calciohatertite

Chemical formula: NaNaCa(CaFe₃+)(As₅+O₄)₃

Calciohatertite is a very rare sodium, calcium, and iron arsenate, found as microscopic, brown crystals in volcanic fumaroles.

## Characteristics Calciohatertite is a complex arsenate from the alluaudite supergroup, with a chemical formula close to Na₂Ca(Ca,Fe³⁺)(Fe³⁺,Mg)₂(AsO₄)₃. It forms very small, hexagonal crystals with a tabular or short prismatic habit, not exceeding 0.2 mm. They usually occur as radial or rosette-like aggregates. The mineral has a characteristic brown color and is valued by collectors specializing in microminerals. ## Physical Properties Calciohatertite crystals are translucent and exhibit a vitreous luster. Due to the microscopic size of the specimens, the Mohs hardness has not been determined. The density of the mineral, calculated from crystallographic data, is approximately 4.21 g/cm³. ## Colors and Varieties The only known color of calciohatertite is brown in various shades. No color varieties or commercial varieties have been distinguished, which is understandable for such a rare mineral. ## History and Name The mineral was described in 2008 by a team of mineralogists led by Nikita V. Chukanov. Its name refers to its chemical composition – with dominant calcium (Latin: *calcius*) – and its structural similarity to hatertite. The type locality, i.e., the first place of discovery, is the Hatert quarry near the Bellerberg volcano in the Eifel mountains in Germany. ## Applications Calciohatertite has no industrial applications. Its significance is purely scientific and for collectors, as a unique representative of the arsenate group.

Properties

Luster: Vitreous
Streak: Light brown
Density: 4.21
Cleavage: None
Transparency: Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of calciohatertite based on visual characteristics is practically impossible and requires advanced analytical techniques, such as energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Clues may include: brown color, mineral associations, and the specific environment of occurrence (volcanic fumaroles). ## Distinguishing from Similar Minerals This mineral can be confused with other brown arsenates occurring in the same environment, e.g., berzeliite, svabite, or other minerals from the alluaudite group. Certain distinction is only possible through chemical and structural analysis. ## Crystal Forms Calciohatertite forms small, hexagonal crystals with a tabular or short prismatic habit. They often occur as radial or rosette-like aggregates on the surface of the host rock.

Geological environment

## Genesis Calciohatertite is a fumarolic mineral. It forms as a result of crystallization from hot, arsenic-rich volcanic gases in fissures and voids within basanite and leucite-tephrite lavas. ## Mineral Associations This mineral co-occurs with other rare products of volcanic exhalations, such as berzeliite, svabite, johillerite, as well as hematite and forsterite. ## Localities The only confirmed occurrence of calciohatertite in the world is its type locality – the Hatert quarry, located near the Bellerberg volcano in the Eifel region (Rhineland-Palatinate, Germany).

Rarity

Extremely rare

For collectors

## Quality Criteria For microminerals, such as calciohatertite, specimens with well-formed, sharp crystals are most highly valued, even if their size is sub-millimeter. The richness of aggregates (e.g., dense, rosette-like clusters) and aesthetic placement on the rock matrix also increase value. The presence of other rare associated minerals is also a significant asset. ## Popular Localities The only specimens available on the collector's market come from the type locality in the Eifel mountains in Germany. They are extremely difficult to acquire and mainly go to specialized collections.

Care and storage

## Cleaning Calciohatertite specimens are extremely small and fragile. They should be cleaned with the utmost care, preferably using compressed air to remove dust. Mechanical cleaning (brushes) and contact with water and chemicals are not recommended. ## What to Avoid As an arsenate, the mineral is potentially toxic – avoid inhaling dust and always wash hands after contact. It should be protected from acids, moisture, and sudden temperature changes. The stability of the mineral is not fully understood, so storage under constant conditions is recommended. ## Storage The safest storage method is to place the specimen in a sealed "micromount" box, away from light, dust, and moisture. The box should be clearly labeled due to the toxicity of arsenic.

Sources

IMA Mineral List (CNMNC)