Vashegyite

Chemical formula: Al<sub>11</sub>(PO<sub>4</sub>)<sub>9</sub>(OH)<sub>6</sub>·38H<sub>2</sub>O

Vashegyite is a rare, hydrated aluminum phosphate, forming characteristic, spherical aggregates with a silky luster.

## Characteristics Vashegyite is a hydrated aluminum phosphate, occurring in the form of delicate, fibrous aggregates. It most often forms spherical or hemispherical aggregates with a radial structure, as well as crusts and veins. The individual "fibers" are actually microscopic crystals. Due to its structure, specimens are very brittle and porous. ## Physical Properties This mineral is very soft, with a Mohs hardness of approximately 2. It is also very light, with a density close to 1.9 g/cm³. It exhibits a silky luster on the fracture surfaces of fibrous aggregates, and can be dull in massive form. It is translucent to opaque. ## Colors and Varieties Vashegyite is typically white, creamy, yellowish, or greenish. The color often depends on impurities and the degree of hydration. No named varieties are distinguished. ## History and Name The mineral was first described in 1909. Its name comes from the discovery locality - the hills in the vicinity of Vashegy (Železník) in Slovakia (then part of Hungary).

Properties

Mohs hardness
2
Luster
Silky
Streak
White
Density
1.91
Cleavage
Perfect on {010}, Good on {100}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Characteristic features of vashegyite include its mode of occurrence (spherical, radially fibrous aggregates), low hardness, lightness, and silky luster. It often occurs in association with other phosphates, such as wavellite. ## Distinguishing from Similar Minerals Vashegyite is sometimes confused with wavellite, which also forms radial aggregates. However, wavellite is significantly harder (3.5-4 on the Mohs scale) and denser. It can also be mistaken for other fibrous secondary minerals, but the hardness test and specific aggregate form are key for identification. ## Crystal Forms The mineral forms microscopic, acicular or fibrous crystals that combine into spherical, radial aggregates, crusts, and earthy masses.

Geological environment

## Genesis Vashegyite is a secondary mineral, forming in the oxidation zones of phosphorus-rich deposits, especially in caves and mines, where phosphate-rich solutions (e.g., from bat guano) react with aluminum-rich rocks. ## Mineral Associations It co-occurs with minerals such as wavellite, variscite, strengite, as well as clay minerals and iron oxides (limonite). ## Localities The most important localities, from which classic specimens originate, is the discovery site - Železník in Slovakia. It is also known from several localities in the United States, including mines in Nevada and Arkansas.

Rarity

Rare

For collectors

## Quality Criteria For collectors, the most valuable specimens are those with well-formed, spherical aggregates with a distinct, radial structure. The purity of color (snow-white) and the size and aesthetics of the aggregates on the rock matrix enhance the specimen's appeal. The integrity of the delicate fibers is also important. ## Popular Localities Classic and most prized specimens come from the historical locality of Železník in Slovakia.

Care and storage

## Cleaning Vashegyite is extremely sensitive to water and chemicals. It should not be washed in water, as it may partially dissolve or lose its cohesion. To remove dust, a very soft brush can be used, or dust can be carefully blown off. ## What to Avoid Contact with water, acids, detergents, and any other liquids must be strictly avoided. The mineral is very soft and brittle, so it should be protected from impacts, scratching, and vibrations. Prolonged exposure to dry air can lead to dehydration and disintegration of the specimen. ## Storage Vashegyite specimens are best stored in closed, padded boxes or display cases to protect them from mechanical damage and dust. Maintaining stable ambient humidity is important to prevent dehydration.

Sources

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