Mendeleevite-(Ce)

Chemical formula: Cs<sub>6</sub>(Ce<sup>3+</sup>,REE,Ca)<sub>30</sub>(Si<sub>70</sub>O<sub>175</sub>)(OH,F,H<sub>2</sub>O)<sub>35</sub>

Mendeleevite-(Ce) is a very rare mineral from the silicate group, characterized by an exceptionally complex chemical composition with cesium and cerium.

## Characteristics Mendeleevite-(Ce) is an extremely rare mineral with a very complex structure and chemical composition, belonging to the ekanite group. It forms small, poorly developed crystals, usually less than 1 mm in size, often occurring as aggregates or irregular grains. It is typically brown or yellowish-brown and exhibits a vitreous luster. ## Physical Properties This mineral is characterized by a Mohs hardness of approximately 5. It is brittle, and its fracture is uneven. The calculated density is about 3.65 g/cm³. It is a translucent mineral. ## Colors and Varieties The observed colors of mendeleevite-(Ce) are various shades of brown, from yellowish-brown to dark brown. No varieties have been distinguished. ## History and Name The mineral's name honors Dmitri Mendeleev (1834-1907), a Russian chemist and creator of the periodic table of elements. The suffix "-(Ce)" indicates the dominant rare earth element in its composition – cerium. The mineral was approved by the IMA in 2010, and its discovery was described in 2011. The discovery locality is the Darai-Pioz Glacier in Tajikistan. ## Applications Due to its extreme rarity and microscopic crystal sizes, mendeleevite-(Ce) has no practical applications. It is of purely scientific interest and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness
5
Luster
Vitreous
Streak
White
Density
3.65
Cleavage
None
Fracture
Uneven
Transparency
Translucent
Crystal system
Cubic

Diagnostic features

## Identification Identification of mendeleevite-(Ce) is impossible without advanced analytical techniques, such as electron spectroscopy (EDS/WDS) and X-ray diffraction (XRD). It is unrecognizable in the field. Visual characteristics, such as brown color and occurrence in a specific geological environment, can only be a preliminary indication. ## Distinguishing from Similar Minerals It can be confused with other rare silicates from the same locality, such as turkestanite, sogdianite, or darapiozite. Definitive differentiation requires chemical analysis, especially to confirm the dominance of cesium and cerium. ## Crystal Forms The mineral forms poorly developed, isometric crystals up to 0.5 mm in size, often as irregular grains and aggregates.

Geological environment

## Genesis It is a hydrothermal mineral associated with alkaline pegmatites. It forms in the late stages of crystallization in an environment rich in rare earth elements, cesium, titanium, and silica. It occurs in quartz veins cutting marbles. ## Mineral Associations This mineral coexists with quartz, microcline, aegirine, polylithionite, turkestanite, and stillwellite-(Ce). ## Localities The only confirmed locality of mendeleevite-(Ce) in the world is its type locality – the Darai-Pioz Glacier in the Alay Mountains, Tajikistan. This is one of the world's most renowned sites for rare minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a mendeleevite-(Ce) specimen is primarily determined by the size and degree of crystal development, which is rare. The most valuable specimens are those where crystals are clearly visible, well-formed, and embedded in a contrasting matrix (e.g., white quartz). Due to its microscopic nature, the richness of the aggregate is also crucial. ## Popular Localities All known specimens come from a single location worldwide: the Darai-Pioz Glacier in Tajikistan. This is the only source of this mineral.

Care and storage

## Cleaning Due to its brittleness and rarity, specimens should only be cleaned if absolutely necessary, using compressed air to remove dust. Contact with water and chemicals should be avoided. ## What to Avoid Avoid ultrasonic cleaners, all acids and bases, and sudden temperature changes. The mineral is brittle, so it should be protected from impacts and scratches. ## Storage Mendeleevite-(Ce) specimens are typically microscopic and stored in specialized "micromount" boxes. They should be kept under stable conditions, away from dust and moisture.

Sources

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