Lukechangite-(Ce)

Chemical formula: Na<sub>3</sub>Ce<sup>3+</sup><sub>2</sub>(CO<sub>3</sub>)<sub>4</sub>F

Lukechangite-(Ce) is a very rare mineral from the carbonate group, forming small, hexagonal crystals with a vitreous luster.

## Characteristics Lukechangite-(Ce) is a hydrated sodium and cerium carbonate. It occurs as very small, hexagonal, tabular or prismatic crystals, rarely exceeding 1 mm in size. It typically forms disseminated aggregates or occurs as single, isolated crystals. It is transparent to translucent, with a vitreous luster. ## Physical Properties This mineral has a hardness of approximately 4.5 on the Mohs scale. It is brittle, and its density is about 3.63 g/cm³. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties Lukechangite-(Ce) is colorless or ranges from pale yellow to yellow. No varieties have been distinguished. ## History and Name The mineral was discovered in the Poudrette quarry at Mont Saint-Hilaire, Quebec (Canada) and described in 1997. Its name honors Luke W. L. Chang (1933–), professor of geology at the University of Maryland, for his contributions to mineralogy and phase chemistry of rare-earth carbonates. The suffix "-(Ce)" refers to the dominant rare-earth element in its composition – cerium. ## Uses Due to its extreme rarity and microscopic crystal sizes, lukechangite-(Ce) has no industrial applications. It is of purely scientific interest and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness
4.5
Luster
Vitreous
Streak
White
Density
3.63
Cleavage
Good on {0001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Hexagonal

Diagnostic features

## Identification Amateur identification of lukechangite-(Ce) is practically impossible due to its microscopic size and occurrence in complex parageneses. Identification requires advanced analytical methods, such as energy-dispersive spectroscopy (EDS/WDS) to confirm chemical composition and X-ray diffraction (XRD) to determine crystal structure. Visually, it can be suspected based on the hexagonal habit of the crystals and co-occurrence with other rare alkaline minerals. ## Differentiation from Similar Minerals It can be confused with other fine-grained rare-earth carbonates, such as bastnäsite-(Ce), parisite-(Ce), or sahamalite-(Ce), which often occur in the same environment. Definitive differentiation is possible only through chemical and structural analysis. ## Crystal Forms It forms hexagonal, tabular or short-prismatic crystals, often terminated by pyramids. It occurs as single, isolated crystals or in small groups.

Geological environment

## Genesis Lukechangite-(Ce) is a hydrothermal mineral, crystallizing in the late stages of nepheline syenite pegmatite evolution. It forms in rock cavities and fractures within sodalite xenoliths or directly in syenites. ## Mineral Associations This mineral co-occurs with many other rare minerals typical of alkaline environments. At the type locality (Mont Saint-Hilaire), it has been found in association with, among others, microcline, albite, aegirine, sodalite, eudialyte, serandite, catapleiite, steenstrupine-(Ce), donneyite-(Y), and sahamalite-(Ce). ## Localities The only confirmed and well-documented occurrence of lukechangite-(Ce) in the world is the Poudrette quarry in Mont Saint-Hilaire, La Vallée-du-Richelieu Regional County Municipality, Quebec, Canada.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of lukechangite-(Ce) specimens is primarily assessed based on the size and development of the crystals, which is a rarity. Most valued are specimens with sharply defined, well-formed crystals of a distinct yellow color, set on a contrasting rock matrix. The richness of association with other rare minerals is also important, as it enhances the scientific and aesthetic value of the specimen. ## Popular Localities The only source of collectible specimens is the type locality – the Poudrette quarry in Mont Saint-Hilaire, Canada. This is one of the most famous mineralogical localities in the world, known for the occurrence of hundreds of unique and rare minerals.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using compressed air to remove dust. Due to the microscopic size of the crystals and their brittleness, any mechanical contact (e.g., with a brush) is highly risky. Cleaning in water or other liquids is not advisable without thorough knowledge of the mineral's properties. ## What to Avoid Avoid contact with acids, which rapidly decompose the mineral with the release of carbon dioxide. Also avoid ultrasonic cleaners, high temperatures, and sudden temperature changes. The crystals are very brittle and susceptible to mechanical damage. ## Storage Lukechangite-(Ce) specimens should be stored under stable conditions, away from dust and vibrations. The best solution is a sealed "micromount" box, which protects delicate crystals from damage and contamination. Avoid exposure to moisture and chemical contaminants.

Sources

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