Hydroniumpharmacoalumite

Chemical formula: (H₃O)Al₄(As₅+O₄)₃(OH)₄·₄.₅H₂O

Hydroniumpharmacoalumite is a very rare aluminum arsenate, named for its chemical composition and its relationship to pharmacoalumite.

## Characteristics Hydroniumpharmacoalumite is a very rare secondary mineral, occurring as small, cubic crystals not exceeding 0.2 mm in size. It typically forms thin coatings or aggregates of microscopic cubes on rock surfaces. Due to the small size of the crystals, its visual features are difficult to observe with the naked eye and require magnification. ## Physical Properties Crystals exhibit a vitreous luster. The mineral is brittle, and its hardness and density have not been precisely determined due to the small amount of available material. ## Colors and Varieties Hydroniumpharmacoalumite is colorless to white. No varieties have been distinguished. ## History and Name The mineral's name, approved in 2012, refers to its chemical composition – the presence of hydronium ions (H₃O) – and its structural and chemical similarity to pharmacoalumite. It was discovered in the dumps of the former mine in Maria-Neustift, Upper Austria. ## Uses Due to its extreme rarity and microscopic size, hydroniumpharmacoalumite has no practical application and is solely an object of scientific interest and for specialized collectors of rare minerals.

Properties

Luster: Vitreous
Streak: White
Cleavage: None
Fracture: Uneven
Transparency: Transparent
Crystal system: Cubic

Diagnostic features

## Identification Identification of hydroniumpharmacoalumite is only possible using advanced laboratory methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). Visually, it is practically indistinguishable from other similar minerals. ## Distinguishing from similar minerals It can be confused with other arsenates from the pharmacoalumite group, such as pharmacoalumite or pharmacosiderite. Differentiation requires specialized chemical analysis to confirm the dominance of the hydronium ion (H₃O) in the structure. ## Crystal forms It forms exclusively microscopic crystals with a cubic habit.

Geological environment

## Genesis Hydroniumpharmacoalumite is a secondary mineral, formed in the oxidation zones of ore deposits rich in arsenic. It forms as a result of the weathering of primary arsenic-bearing minerals in a low pH environment. ## Mineral associations It co-occurs with other secondary arsenates, such as pharmacoalumite, pharmacosiderite, scorodite, and also with quartz. ## Localities The only confirmed occurrence of this mineral is its type locality – the dumps of the former mine in Maria-Neustift, in the region of Upper Austria, Austria.

Rarity

Extremely rare

For collectors

## Quality criteria For micromineral collectors, the value of a specimen depends on the size and quality of the cubic crystals (sharpness of edges, lack of damage) and their abundance on the rock matrix. The aesthetics of the entire composition and the presence of associated minerals are also important. ## Popular localities The only source of specimens is the type locality in Austria, which makes them extremely difficult to acquire.

Care and storage

## Cleaning Due to their microscopic nature and fragility, specimens of hydroniumpharmacoalumite should not be cleaned mechanically or chemically. The safest way to remove dust is with a photographic air blower. ## What to avoid Avoid contact with water, chemicals, ultrasound, and sudden temperature changes. The crystals are very small and brittle, susceptible to mechanical damage. ## Storage Specimens should be stored in stable conditions, in closed "micromount" boxes, to protect them from dust, moisture, and physical damage.

Sources

IMA Mineral List (CNMNC)