Ancylite-(Ce)

Chemical formula: Ce<sup>3+</sup>Sr(CO<sub>3</sub>)<sub>2</sub>(OH)·H<sub>2</sub>O

Ancylite-(Ce) is a rare mineral from the carbonate group, forming small, prismatic or pyramidal crystals with colors ranging from yellow to brown.

## Characteristics Ancylite-(Ce) is a hydrated strontium and cerium carbonate, belonging to the ancylite group. It typically forms very small, prismatic, pseudo-octahedral, or steeply pyramidal crystals, rarely exceeding a few millimeters. They often occur as aggregates in vugs and small rock fissures. The crystals can be striated. ## Physical Properties This mineral is characterized by a Mohs hardness of 4-4.5 and is relatively brittle. Its luster is most often vitreous, and on fracture surfaces, it can be greasy. It is a translucent mineral, less commonly transparent. Its density is approximately 3.96 g/cm³. ## Colors and Varieties Ancylite-(Ce) exhibits colors ranging from pale yellow, through yellowish-brown, orange-brown, reddish-brown, to gray or almost black. The coloration is often unevenly distributed. No named varieties are distinguished. ## History and Name The mineral's name comes from the Greek word *ankylos* (curved), referring to the typical, rounded form of its crystals. The suffix -(Ce) indicates the dominance of cerium as the rare earth element in its composition. The mineral was first described in 1899 by Gustav Flink based on specimens found in the Ilimaussaq complex in Greenland. ## Uses Due to its rarity and small crystal size, ancylite-(Ce) has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and micromounts.

Properties

Mohs hardness
4-4.5
Luster
Vitreous, Greasy
Streak
White
Density
3.96
Cleavage
Good on {101}, poor on {010}
Fracture
Uneven to sub-conchoidal
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Ancylite-(Ce) is primarily identified by its characteristic crystal habit – short, prismatic, pseudo-octahedral, or steeply pyramidal, often with rounded faces. Its typical colors (shades of yellow and brown) and occurrence in vugs and fissures of alkaline rocks are also diagnostic. Reaction with hydrochloric acid confirms it is a carbonate. ## Differentiation from Similar Minerals It can be confused with other minerals from the ancylite group, from which it can only be distinguished by advanced chemical analyses (EDS/WDS) to determine the dominant rare earth element. Visually, it may resemble some carbonates, such as burbankite or parisite, but differs from them in crystal habit and occurrence environment. ## Crystal Forms Crystals are typically short-prismatic, pseudo-octahedral, or dipyramidal, often with modified and rounded faces, giving them a barrel-shaped appearance. It occurs as single, overgrown crystals or small groups of them in vugs.

Geological environment

## Genesis Ancylite-(Ce) is a hydrothermal mineral. It forms in the late stages of crystallization in nepheline syenite pegmatites and in carbonatites. It crystallizes in fissures and rock cavities from solutions rich in rare earth elements, strontium, and carbonates. ## Mineral Associations It frequently co-occurs with other minerals typical of alkaline rocks, such as eudialyte, aegirine, microcline, albite, nepheline, natrolite, catapleiite, lorenzenite, as well as with other rare earth minerals, e.g., minerals from the bastnäsite and synchysite groups. ## Localities The most important and classic locality for ancylite-(Ce) is the Ilimaussaq alkaline complex in Greenland. Significant specimens also come from the Khibiny and Lovozero massifs on the Kola Peninsula in Russia. Other known localities include Mont Saint-Hilaire in Quebec (Canada) and alkaline complexes in Norway (Langesundsfjorden) and the USA (Bearpaw Mountains, Montana).

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp, and undamaged crystals of intense orange-brown or yellow color. Rich vugs with numerous crystals are also highly valued. A contrasting, light rock matrix (e.g., white albite or natrolite) significantly enhances the visual appeal and value of the specimen. Due to the small size of the crystals, their perfect form is crucial. ## Popular Localities Specimens from the Khibiny and Lovozero massifs in Russia and from Mont Saint-Hilaire in Canada are considered among the best in the world. Greenland, as the type locality, provides historically important specimens, which are, however, less available on the collector's market.

Care and storage

## Cleaning Ancylite-(Ce) specimens are usually small and brittle, so they should be cleaned with utmost care. The safest method is to use a soft brush to remove dust. If necessary, the specimen can be gently rinsed with distilled water, then thoroughly dried with compressed air or left to air dry completely. ## What to Avoid Ancylite-(Ce) is a carbonate, which means it reacts vigorously with acids (e.g., hydrochloric acid), dissolving completely. Contact with any chemicals should be strictly avoided. The mineral is also sensitive to mechanical damage and high temperatures. ## Storage The best way to store ancylite-(Ce) specimens is in small, sealable "micromount" boxes, which protect them from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight and store in stable temperature conditions.

External references

Sources

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