Fluornatrocoulsellite
Chemical formula: (Na<sub>1.5</sub>Ca<sub>0.5</sub>)(Mg<sub>1.5</sub>Al<sub>0.5</sub>)F<sub>6</sub>F
Fluornatrocoulsellite is an extremely rare sodium, calcium, and magnesium fluoride, forming colorless, acicular crystals in volcanic fumaroles.
Description
## Characteristics Fluornatrocoulsellite is a halide mineral belonging to the coulsellite group. It is the fluorine and sodium analog of coulsellite. It forms very small, colorless, and transparent crystals with a prismatic or acicular habit, reaching a maximum length of 0.3 mm. It occurs as radial or chaotically arranged aggregates, growing on volcanic crust. ## Physical Properties The hardness of the mineral has been calculated to be approximately 4 on the Mohs scale. Its measured density is 2.99 g/cm³. It exhibits a vitreous luster and is completely transparent. ## Colors and Varieties This mineral is colorless. No colored varieties or trade names are known. ## History and Name The name refers to its chemical composition – the dominance of fluorine (Fluoro) and sodium (Natro) – and its structural relationship to coulsellite. It was officially described as a new mineral species in 2022 by a team of mineralogists led by Igor V. Pekov. It was discovered in samples from the fumaroles of Tolbachik volcano in Kamchatka. ## Applications Fluornatrocoulsellite has no practical applications. Due to its extreme rarity and microscopic size, it is solely an object of scientific interest and a valuable acquisition for specialized collectors of micromount minerals.
Diagnostic features
## Identification Correct identification of fluornatrocoulsellite is impossible without advanced analytical techniques, such as electron microprobe (EDS) and X-ray diffraction (XRD). Indicative features of its possible presence include: microscopic, colorless, acicular crystals, occurrence in volcanic fumaroles, and co-occurrence with other rare fluorides. ## Distinguishing from Similar Minerals It can be easily confused with many other colorless sublimation minerals, such as sellaite, ralstonite, or other fluorides found in the same environment. Definitive distinction requires chemical and structural analysis. ## Crystal Forms Crystals are elongated, prismatic to acicular. They typically form small, radial aggregates or disordered aggregates on the surface of the host rock.
Geological environment
## Genesis Fluornatrocoulsellite is a product of the sublimation of volcanic gases in high-temperature fumaroles (at 450-500°C). It forms as a result of the reaction of fluorine-rich exhalations with basaltic volcanic crust. ## Mineral Associations It co-occurs with other fumarolic minerals, such as sellaite, gagarinite-(Y), ralstonite, usovite, hematite, and cassiterite. ## Localities The only known locality in the world is its type locality – Arsenatnaya fumarole, located on the second cinder cone of Tolbachik volcano on the Kamchatka Peninsula, Russia.
Rarity
Extremely rare
Collector aspects
## Quality Criteria For micromount minerals such as fluornatrocoulsellite, the value of a specimen is determined by the abundance (number and density of crystals on the matrix), sharpness and development of crystals, and the presence of rare associated minerals. Due to their size, aesthetics are evaluated under a microscope. ## Popular Localities All known specimens come from a single location in the world – Tolbachik volcano in Kamchatka. This locality is inaccessible to the typical collector.
Care and storage
## Cleaning Specimens are extremely delicate and small. Cleaning is not recommended. If necessary, a stream of compressed air from a safe distance or a soft brush can be used very carefully to remove dust. ## What to Avoid As a fluoride formed in a volcanic environment, it should be protected from moisture, water, and acids, which can damage it. Avoid sudden temperature changes and direct contact with chemicals. ## Storage The safest way to store it is to place the specimen in a closed, padded "micromount" box, which protects it from mechanical damage, dust, and humidity fluctuations.