Fassinaite

Chemical formula: Pb₂+₂(CO₃)(S₆+O₃S₂-)

An extremely rare mineral from the carbonate group, being a lead thiosulfate-carbonate, found exclusively in one location worldwide.

## Characteristics Fassinaite is a lead mineral with a unique chemical composition, combining carbonate and thiosulfate groups. It occurs as very small, prismatic crystals, elongated in one direction, rarely exceeding 0.2 mm in length. These crystals form fan-shaped, radial, or nearly parallel aggregates and clusters. It is colorless to white and exhibits a strong, adamantine luster. ## Physical Properties The mineral is transparent, and its streak is white. The luster is described as adamantine. Hardness has not been measured due to the small size of the crystals, but it is estimated to be around 2.5-3 on the Mohs scale. The density calculated based on chemical composition and crystal structure is 6.45 g/cm³. ## Colors and Varieties Fassinaite is colorless or white. No colored varieties or trade names are known. ## History and Name The mineral was described in 2011 by a team of mineralogists led by Paolo Orlandi. Its name honors the Fassina family (Bruno Fassina and his son Flavio), well-known Italian mineral collectors from Padua, who found the first samples. The type locality and only known occurrence is the Gara Gola mine in Tuscany, Italy. ## Applications Due to its extreme rarity and microscopic size, fassinaite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized micromount mineral collectors.

Properties

Luster: Adamantine
Streak: White
Density: 6.45
Cleavage: None
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Amateur identification of fassinaite is practically impossible. Due to its microscopic size and occurrence alongside other colorless secondary lead minerals, its definitive identification requires advanced analytical techniques such as X-ray diffraction (XRD) and chemical microanalysis (EDS). ## Distinguishing from Similar Minerals This mineral can be easily confused with associated cerussite and anglesite, which are also colorless or white, secondary lead minerals with strong luster. Differentiation is almost exclusively possible based on chemical composition analysis, confirming the presence of the thiosulfate group. ## Crystal Forms It forms tiny, acicular or prismatic crystals, usually grouped into radial or fan-shaped aggregates on the surface of the host rock.

Geological environment

## Genesis Fassinaite is a secondary mineral that forms in the oxidation zone of polymetallic ore deposits (Cu-Pb-Zn). It forms at low temperatures as a result of reactions between lead-rich solutions and thiosulfate ions, originating from the weathering of sulfides, in a carbonate rock (dolomite) environment. ## Mineral Associations It most commonly co-occurs with other secondary lead minerals such as anglesite and cerussite. It is also accompanied by galena, sphalerite, pyrite, wulfenite, hemimorphite, and hydrozincite. ## Localities The only confirmed locality of fassinaite in the world is its type locality - the Gara Gola mine, near Montecatini Val di Cecina, in the province of Pisa, Tuscany, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria For micromount minerals like fassinaite, specimens with well-formed, sharp, and transparent crystals are most highly valued. The aesthetics of the entire aggregate are also important – its form (e.g., a perfectly radial rosette) and contrasting placement on a small rock matrix. The richness of the cluster and association with other rare minerals also increase its collector's value. ## Popular Localities All known fassinaite specimens come from one location in the world: the Gara Gola mine in Italy. This is the only locality from which collectors can obtain this mineral.

Care and storage

## Cleaning Fassinaite specimens are extremely small and delicate. Mechanical cleaning or the use of any liquids is absolutely discouraged. The only permissible method for dust removal is the very gentle use of a photographic air blower or a can of compressed air from a distance. ## What to Avoid As a lead carbonate, this mineral is sensitive to acids, which cause its rapid decomposition. Contact with chemicals, sudden temperature changes, and humidity should be avoided. Specimens should not be exposed to direct sunlight. ## Storage Fassinaite should be stored exclusively in specialized micromount boxes that protect it from dust, shocks, and humidity changes. This is the best way to secure and display such small and fragile specimens.

Sources

IMA Mineral List (CNMNC)