Guastoniite-(Y)

Chemical formula: Pb²⁺₄(YCa)(Si₈B₄O₂₈)F

Guastoniite-(Y) is a very rare lead, yttrium, and calcium borosilicate, forming colorless, tabular crystals, discovered in Tajikistan.

## Characteristics Guastoniite-(Y) is an extremely rare mineral from the hyalotekite group, belonging to the borosilicate class. Its complex chemical composition is dominated by lead, yttrium, calcium, silicon, and boron. It forms very small, colorless, transparent crystals with a tabular habit, reaching sizes up to 0.2 mm. It exhibits white fluorescence under ultraviolet light. Due to its extreme rarity and small crystal size, it is a mineral known primarily within the scientific community. ## Physical Properties Guastoniite-(Y) crystals are characterized by a vitreous luster. They are transparent and colorless. Hardness and density have not been precisely measured due to the small amount of available material. ## Colors and Varieties This mineral is colorless. No varieties have been distinguished. ## History and Name Guastoniite-(Y) was first described in 2023 by an international team of researchers (Frank C. Hawthorne et al.). Its name honors the Italian mineral collector and micromounter, Arrigo Guastoni (born 1956), for his contributions to mineralogy. The "(Y)" suffix in the name indicates the dominance of yttrium in a specific structural site, in accordance with the naming rules for minerals containing rare earth elements. ## Applications Guastoniite-(Y) has no industrial applications. Its significance is purely scientific and collectible, especially for collectors specializing in type minerals (discovered in a specific locality) and micromounts.

Properties

Luster
Vitreous
Transparency
Transparent
Crystal system
Triclinic

Diagnostic features

## Identification Identification of guastoniite-(Y) is possible only through advanced analytical methods, such as Raman spectroscopy, X-ray diffraction (XRD), and chemical analysis using an electron microprobe (EDS/WDS). Visual identification in the field or even in a collection is impossible due to its appearance and co-occurrence with other similar minerals. ## Distinguishing from Similar Minerals Guastoniite-(Y) is very similar to other minerals from the hyalotekite group, such as hyalotekite or kapranovaite-(Y). Differentiation requires specialized structural and chemical studies to determine the exact composition and unit cell parameters. ## Crystal Forms This mineral forms very small, thin, tabular crystals, often aggregated into small clusters.

Geological environment

## Genesis Guastoniite-(Y) forms under specific conditions within nepheline syenites and associated pegmatites that have undergone sodic metasomatism. It is a product of hydrothermal processes occurring in an environment rich in rare earth elements, boron, and fluorine. ## Mineral Associations This mineral co-occurs with other rare minerals in the Dara-i-Pioz massif. Its typical associations include quartz, microcline, aegirine, polylithionite, eudialyte, kapranovaite-(Y), and turkestanite. ## Localities The only confirmed locality of guastoniite-(Y) in the world is its type locality – the Dara-i-Pioz massif in Tajikistan. This is one of the world's most famous sites for rare minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a guastoniite-(Y) specimen is primarily determined by the presence of well-formed, identifiable crystals, even if they are microscopic in size. Due to its extreme rarity, every analytically confirmed specimen is extremely valuable. An additional advantage is the abundance of associated minerals on the same sample. ## Popular Localities The only source of specimens is the Dara-i-Pioz massif in Tajikistan. Material from this locality is extremely difficult to obtain and appears on the collector's market sporadically.

Care and storage

## Cleaning Due to the extreme rarity and small size of the crystals, guastoniite-(Y) specimens should not be cleaned mechanically or chemically. Any contaminants should be left undisturbed. ## What to Avoid Avoid any contact with chemicals, ultrasound, and sudden temperature changes. Specimens must not be subjected to any physical tests (e.g., scratch tests) that could irreversibly damage them. ## Storage Specimens of this mineral, typically in the form of micromounts, should be stored exclusively in specialized, airtight boxes (so-called micromount boxes) that protect against dust, moisture, and mechanical damage. Avoid exposure to direct sunlight.

External references

Sources

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