Nannoniite

Chemical formula: Al₂(OH)₅F

An extremely rare aluminum fluoride, closely related to ralstonite, occurring as microscopic, colorless crystals.

## Characteristics Nannonite is an exceptionally rare halide mineral, chemically classified as a basic aluminum fluoride. It is a member of the ralstonite group and its aluminum analogue. It forms microscopic, octahedral crystals, typically not exceeding 20 micrometers in size, which can combine into small aggregates. Due to its size, it is a mineral accessible only to advanced micro-collectors. ## Physical Properties Nannonite crystals are colorless and transparent, with a vitreous luster. Hardness and density have not been precisely measured due to the small size of the crystals, but can be estimated based on analogy with ralstonite. The mineral does not exhibit fluorescence under ultraviolet light. ## History and Name The mineral was approved by the International Mineralogical Association (IMA) in 2019 under number IMA2019-031. Its name honors the Italian mineralogist and collector Roberto Nannoni (born 1944) from the Museo di Mineralogia in Scandicci, Florence, in recognition of his contribution to mineralogy, especially in the study of minerals from Tuscany. It was discovered in samples originating from the Baveno granite quarry, in Piedmont, Italy.

Properties

Mohs hardness
2-3
Color
colourless to white
Luster
Vitreous
Streak
white
Density
2.492
Cleavage
{001}
Fracture
Conchoidal
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of nannonite is possible only through advanced analytical methods, such as Raman spectroscopy and chemical analysis using an electron microprobe (EDS). Visual identification is impossible due to its microscopic size and lack of characteristic macroscopic features. ## Distinguishing from similar minerals Nannonite is practically indistinguishable visually from other minerals of the ralstonite group, such as ralstonite itself or hydrokenoralstonite. Differences between them can only be determined based on precise chemical composition analysis, particularly the aluminum to magnesium ratio and the presence of water. ## Crystal forms The mineral forms only very small, well-formed, regular crystals with an octahedral habit, not exceeding 20 micrometers in size.

Geological environment

## Genesis Nannonite forms as a result of hydrothermal processes in the late stage of crystallization in miarolitic cavities (geodes) in granites. It crystallizes from aluminum- and fluorine-rich solutions under low-temperature conditions. ## Mineral associations At the type locality (Baveno, Italy), it co-occurs with quartz, orthoclase, albite, mica, ralstonite, gearksutite, and fluorite. ## Localities The only confirmed and described locality of nannonite in the world is the Seula granite quarry, near the town of Baveno, in the province of Cusio-Ossola, Piedmont region, Italy.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of a nannonite specimen is assessed based on the sharpness and size of the microscopic crystals and the abundance of its occurrence on the rock matrix. The most desirable specimens are those with numerous, well-formed octahedra, clearly visible under a microscope. The presence of associated minerals, such as ralstonite, can increase the scientific and collector value of the specimen. ## Popular localities The only source of specimens is the type locality – the granite quarry in Baveno, Italy, known for the occurrence of rare minerals in miarolitic cavities.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Any contact with water or chemicals is absolutely inadvisable and can destroy the microscopic crystals. ## What to avoid Avoid all liquids, ultrasonics, chemicals, high temperatures, and vibrations. The mineral is extremely delicate and sensitive to environmental changes. ## Storage Nannonite specimens should be stored exclusively in specialized micromount boxes, protecting them from dust, moisture, and mechanical damage. Frequent opening of the container should be avoided.

External references

Sources

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