Ilímaussite-(Ce)

Chemical formula: (Ba,Na)₁₀K₃Na₄.₅Ce₃+₅(Nb₅+,Ti₄+)₆O₆(Si₁₂O₃₆)(Si₉O₁₈)(O,OH)₂₄

A very rare, complex silicate of barium, sodium, and cerium, forming small, hexagonal crystals in nepheline syenites of Greenland.

## Characteristics Ilímaussite-(Ce) is a very complex and rare mineral from the silicate group, with a unique structure containing two different types of silicate rings (Si₉O₁₈ and Si₁₂O₃₆). It occurs as small, well-formed crystals, usually tabular or short-prismatic. Its appearance is inconspicuous, and its significance is primarily scientific and for collectors. ## Physical Properties The mineral's hardness on the Mohs scale is 5. It has a density of 3.65 g/cm³, a vitreous luster, and is transparent to translucent. It exhibits perfect cleavage in one plane, making it brittle and susceptible to mechanical damage. ## Colors and Varieties The observed colors of ilímaussite-(Ce) are usually pale and range from light brownish-yellow to pale pink and lilac. No named varieties of this mineral have been distinguished. ## History and Name The mineral was first described in 1965 by E. I. Semenov, M. E. Kazakova, and V. J. Bukin. Its name comes from its discovery locality – the famous Ilímaussaq alkaline complex in southern Greenland. The suffix -(Ce) in the name indicates that cerium is the dominant rare-earth element in its composition. ## Uses Ilímaussite-(Ce) has no industrial applications. It is of interest only in scientific circles and among collectors specializing in rare minerals and micromounts.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 3.65
Cleavage: Perfect on {0001}
Transparency: Transparent to translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Amateur identification of ilímaussite-(Ce) is practically impossible. Key indicators include: hexagonal crystal form, pale color (yellowish, pink), vitreous luster, and perfect basal cleavage. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS). ## Differentiation from Similar Minerals This mineral can be confused with other rare silicates found in the same environment, such as eudialyte, steenstrupine-(Ce), or ussingite. Differentiation is based on subtle differences in crystal form, color, and physical properties, but final confirmation always requires laboratory analysis. ## Crystal Forms It forms small (usually less than 1 mm), hexagonal crystals with tabular, platy, or short-prismatic habits. It occurs singly or in small groups, overgrown on other minerals.

Geological environment

## Genesis Ilímaussite-(Ce) is a mineral of magmatic origin, crystallizing in the late stages of evolution of highly differentiated alkaline magmas. It forms in nepheline syenite pegmatites, under conditions of extreme silica deficiency and high concentrations of rare-earth elements, niobium, and barium. ## Mineral Associations It co-occurs with a rich assemblage of rare alkaline minerals, characteristic of the Ilímaussaq complex. The most common associations include: aegirine, albite, analcime, arfvedsonite, eudialyte, lorenzenite, microcline, nepheline, sodalite, steenstrupine-(Ce), and ussingite. ## Localities This is a mineral with extremely restricted occurrence. The main and essentially only confirmed locality is the Ilímaussaq intrusive complex (in particular the Taseq slope area) in the Kujalleq region of southern Greenland.

Rarity

Extremely rare

For collectors

## Quality Criteria In the case of such a rare mineral, occurring only as microscopic specimens, the main quality criterion is the degree of crystal development and the sharpness of its edges. The most valued are single, undamaged crystals with a distinct, hexagonal form, set on a contrasting matrix (e.g., on white albite or analcime). Size matters – any crystal exceeding 1 mm is considered exceptional. Transparency and intensity of color also increase the value of the specimen. ## Popular Localities The only source of ilímaussite-(Ce) specimens is its type locality – the Ilímaussaq complex in Greenland. Specimens from this location are the standard for this mineral species.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. Distilled water can be used, but prolonged soaking should be avoided. Due to its brittleness and perfect cleavage, ultrasonic cleaning is absolutely forbidden. ## What to Avoid The mineral is very brittle and prone to delamination along the cleavage plane, so it should be protected from impacts, falls, and vibrations. Contact with acids and other aggressive chemicals should be avoided. ## Storage The safest way to store specimens is to place them in a padded "micromount" box, which protects them from mechanical damage and dust. It does not require special conditions regarding light or humidity.

Sources

IMA Mineral List (CNMNC)