Oskarssonite

Chemical formula: AlF₃

Oskarssonite is a natural, hexagonal form of aluminum fluoride (AlF₃), occurring as microscopic crystals in volcanic fumaroles.

## Characteristics Oskarssonite is a natural form of aluminum fluoride. It occurs as colorless, hexagonal or trigonal crystals, not exceeding 200 micrometers in size. These crystals form aggregates or coatings on volcanic ash. Due to their microscopic size, the visual features of individual crystals are discernible only with advanced equipment, such as a scanning electron microscope (SEM). ## Physical Properties Oskarssonite crystals exhibit a vitreous luster. They are transparent and colorless. The density calculated from crystallographic data is 3.10 g/cm³. Hardness has not been determined due to the microscopic size of the crystals. ## History and Name The mineral was approved by the International Mineralogical Association (IMA) in 2011 under number 2011-085. Its name honors the Icelandic chemist and geochemist, Niels Oskarsson (1947–2010), in recognition of his contributions to research on volcanic gases and processes occurring in fumaroles. The discovery was made on material from the Hekla volcano in Iceland. ## Uses Oskarssonite has no commercial or industrial applications. Its significance is purely scientific and as a collector's item, as a rare, naturally occurring aluminum fluoride.

Properties

Luster: Vitreous
Streak: White
Density: 3.10
Cleavage: None
Fracture: Uneven
Transparency: Transparent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of oskarssonite is impossible without specialized analytical equipment. It requires the use of a scanning electron microscope (SEM) with EDS analysis to confirm chemical composition (presence of only aluminum and fluorine) and X-ray diffraction (XRD) to determine the crystal structure. Visually, it appears as microscopic, colorless crystals on volcanic ash. ## Distinguishing from Similar Minerals It can be confused with other microscopic volcanic sublimation products, such as ralstonite or sal ammoniac. Differentiation is based solely on chemical and structural analysis. Oskarssonite is distinguished by its simple composition (AlF₃). ## Crystal Forms It forms hexagonal, tabular, or prismatic crystals, often grouped into rosette-like or chaotic aggregates. Observed crystallographic forms include prism faces {1010} and pinacoid {0001}.

Geological environment

## Genesis Oskarssonite forms by direct sublimation from fluorine-rich volcanic gases in the high-temperature environment of fumaroles. It crystallizes at temperatures around 600-650°C on the surface of volcanic ash and lava. ## Mineral Associations It co-occurs with other fumarolic minerals, such as hematite, ralstonite, jarosite, and amorphous silica and aluminosilicates. ## Localities The only confirmed locality of oskarssonite in the world (type locality) are fumaroles on a lava field formed during the 1991-2000 eruption of Hekla volcano in southern Iceland.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, oskarssonite is primarily valued for the abundance and quality of crystals on the matrix. The most desirable specimens are those with numerous, well-formed, sharp crystals forming photogenic groups. The size of individual crystals, although always microscopic, is also important – larger crystals (above 100 µm) are more prized. Analytical confirmation of the specimen is also crucial. ## Popular Localities The only source of oskarssonite specimens is its type locality – Hekla volcano in Iceland. Material from this location is extremely rare on the collector's market.

Care and storage

## Cleaning Oskarssonite specimens, due to their microscopic nature and delicate substrate (volcanic ash), should not be cleaned in a traditional manner. Any attempts to use water, compressed air, or brushes may damage or dislodge the crystals. ## What to Avoid Avoid any contact with water, chemicals, and vibrations. Specimens are extremely sensitive to mechanical damage. Store away from moisture, which can react with associated minerals. ## Storage Store exclusively in stable, sealed "micromount" containers, protecting them from dust, moisture, and shocks. Display is only possible under a microscope.

External references

https://www.mindat.org/min-43853.html