Atelisite-(Y)

Chemical formula: Y<sub>4</sub>Si<sub>3</sub>O<sub>8</sub>(OH)<sub>8</sub>

Atelisite-(Y) is a very rare yttrium silicate, forming colorless to white, tabular crystals with a pearly luster.

## Characteristics Atelisite-(Y) is a hydrated yttrium silicate, belonging to the group of rare minerals. It occurs as very small, tabular or platy crystals, rarely exceeding 0.3 mm in length. The crystals are usually colorless, white, or pale gray and exhibit a pearly luster on cleavage surfaces. Due to its small size and rarity, it is a mineral known mainly in scientific and specialized circles. ## Physical Properties Atelisite-(Y) crystals are very soft, with a Mohs hardness of only 2. They are characterized by perfect cleavage in one direction, which, combined with the pearly luster, is its distinguishing feature. The mineral is transparent to translucent. Its calculated density is approximately 3.85 g/cm³. ## History and Name The mineral's name comes from the Greek word *ἀτελής* (*atelḗs*), meaning "incomplete" or "unfinished," referring to the fact that its crystal structure was not fully determined at the time of its description. The -(Y) suffix indicates yttrium as the dominant rare-earth element in its composition. The mineral was approved by the IMA in 1998, and its discoverers and authors of the description are G. Della Ventura, F. Bellatreccia, G. C. Parodi, and G. C. Piccinini. The type locality is the Baveno granite quarry in the Verbano-Cusio-Ossola province, Italy.

Properties

Mohs hardness
2
Luster
Pearly
Streak
White
Density
3.85
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Atelisite-(Y) is difficult to identify visually due to the small size of its crystals. Key features include its occurrence in miarolitic cavities in granites, very low hardness (2 on the Mohs scale), perfect cleavage in one direction, and pearly luster. Final identification requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS). ## Distinguishing from Similar Minerals It can be confused with other microscopic secondary minerals found in granitic miaroles, such as micas (e.g., muscovite) or zeolites. It is distinguished from them by its specific chemical composition (dominance of yttrium) and unique crystallographic properties, which can only be studied under laboratory conditions. ## Crystal Forms It forms very small, thin, tabular or platy crystals, often arranged in small, rosette-like or radial aggregates. The crystals are elongated along one axis and flattened.

Geological environment

## Genesis Atelisite-(Y) is a hydrothermal mineral. It forms in the late stage of granite crystallization, in miarolitic cavities and fractures, where it crystallizes from residual, rare-earth-rich aqueous solutions. ## Mineral Associations At the type locality (Baveno, Italy), it co-occurs with minerals such as quartz, albite, microcline, muscovite, fluorite, as well as other rare yttrium and lanthanide minerals, e.g., gadolinite-(Y) and kainosite-(Y). ## Localities This is an extremely rare mineral, known from only a few localities worldwide. Besides the type locality in the Baveno granite quarry in Italy, its occurrence has also been reported in Norway (e.g., in pegmatites in the Tysfjord area) and in Switzerland (in the Alps in the Binn Valley).

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of atelisite-(Y) specimens is primarily assessed based on the abundance and development of microscopic crystals within the rock cavity. The most valued specimens are those with clearly visible, well-formed, though still small, crystalline aggregates, contrasting with the matrix (e.g., with quartz or fluorite). Due to the nature of the mineral, purity and color are of secondary importance. ## Popular Localities The only source of specimens of collector's significance is the type locality – the Baveno granite quarry in Italy. Specimens from this location are highly sought after by collectors specializing in rare minerals and so-called "micromounts."

Care and storage

## Cleaning Due to its extreme rarity, small size, and low hardness, atelisite-(Y) specimens are practically not subject to cleaning. Any attempts at mechanical cleaning may damage the delicate crystals. If it is necessary to remove loose dust, compressed air can be used from a safe distance. ## What to Avoid Avoid contact with any chemicals, acids, and detergents. The mineral is very soft, so it should be protected from scratches and vibrations. It should not be cleaned with ultrasound or steam. Avoid sudden temperature changes. ## Storage Specimens should be stored exclusively in specialized, padded "micromount" boxes, protecting them from mechanical damage, dust, and light. It is best to store them under stable room conditions.

Sources

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