Polezhaevaite-(Ce)

Chemical formula: NaSrCe<sup>3+</sup>F<sub>6</sub>

Polezhaevaite-(Ce) is an extremely rare fluoride of sodium, strontium, and cerium, forming microscopic, colorless grains in pegmatites of the Khibiny Massif.

## Characteristics Polezhaevaite-(Ce) is a halide group mineral that is visually unremarkable. It occurs as very small, anhedral (irregular) grains, not exceeding 0.3 mm in size. These grains are typically intergrown with other pegmatite minerals. Due to its size and lack of well-formed crystals, it is primarily of interest to specialized collectors (micromounters) and scientists. ## Physical Properties The mineral is transparent and exhibits a vitreous luster. Its density, calculated from its chemical composition and unit cell parameters, is 4.58 g/cm³. The Mohs hardness has not yet been determined. ## Colors and Varieties Polezhaevaite-(Ce) is colorless. No colored or commercial varieties are known. The "-(Ce)" suffix in the name indicates that cerium is the dominant rare earth element in its structure. ## History and Name The mineral was approved by the International Mineralogical Association (IMA) in 2018. Its name honors Anna Polezhaeva (born 1956), a Russian mineralogist and chemist from the Kola Science Centre of the Russian Academy of Sciences, for her contributions to the study of minerals from the Kola Peninsula region. ## Uses Due to its extreme rarity and occurrence in microscopic quantities, polezhaevaite-(Ce) has no practical applications. It is of scientific and collecting interest only.

Properties

Luster
Vitreous
Streak
White
Density
4.58
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of polezhaevaite-(Ce) based on visual characteristics is impossible. It is a colorless, vitreous grain without distinctive external features. Definitive identification requires advanced analytical techniques, such as X-ray microanalysis (EDS/WDS), to confirm its unique chemical composition (presence of sodium, strontium, cerium, and fluorine in appropriate proportions). ## Distinguishing from Similar Minerals In its natural environment (Khibiny pegmatites), it can be confused with many other colorless minerals, such as fluorite, quartz, sodalite, or villiaumite. Differentiation from these is possible only through chemical analysis. ## Crystal Forms This mineral does not form well-developed crystals. It occurs exclusively as anhedral (irregular), rounded grains.

Geological environment

## Genesis Polezhaevaite-(Ce) forms in the unique environment of highly alkaline (hyperagpaitic) pegmatites, associated with nepheline syenite intrusions. Its only known locality is within the Khibiny Massif on the Kola Peninsula. ## Mineral Associations This mineral co-occurs with a rich assemblage of minerals typical of Khibiny pegmatites. The most important include villiaumite, aegirine, microcline, nepheline, sodalite, lomonosovite, eudialyte, and shcherbakovite. ## Localities The only confirmed occurrence (type locality) of polezhaevaite-(Ce) in the world is the Koashva mine outcrop in the Khibiny Massif, on the Kola Peninsula (Murmansk Oblast, Russia).

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the collector's value of a polezhaevaite-(Ce) specimen depends on several factors. The most important is certainty of identification, confirmed by a reliable source. The richness of the specimen (quantity and size of polezhaevaite grains) and the aesthetics and quality of associated minerals are also important. Specimens with clearly visible, though irregular, grains on a contrasting background are most desirable. ## Popular Localities The only specimens available on the collector's market come from the type locality - the Koashva mine on the Kola Peninsula in Russia.

Care and storage

## Cleaning Specimens of polezhaevaite-(Ce) should be cleaned with the utmost care, only if necessary. It is recommended to use a soft brush to remove dust. If wet cleaning is required, use only distilled water. Avoid ultrasonic cleaners, which can damage the delicate mineral grains. ## What to Avoid As a fluoride, the mineral may be sensitive to acids. Avoid contact with all chemicals. It must also be protected from thermal shock and mechanical damage, which are very likely due to its occurrence as small, intergrown grains. ## Storage Polezhaevaite-(Ce) specimens are typically micromounts and should be stored in specialized "micromount" boxes that protect them from dust and damage. Stable environmental conditions should be ensured, away from sources of moisture and extreme temperatures.

Sources

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