Calcioancylite-(La)

Chemical formula: (LaCa)(CO₃)₂(OH)(H₂O)

A rare mineral from the carbonate group, a lanthanum and calcium analog of ancylite, forming small, pink crystals.

## Characteristics Calcioancylite-(La) is a rare mineral belonging to the carbonate group, specifically the ancylite group. It is a hydrated calcium and lanthanum carbonate. It forms very small, prismatic or dipyramidal crystals, rarely exceeding 1 mm in length. It usually occurs as single crystals or small aggregates grown on other minerals in rock cavities. ## Physical Properties This mineral is characterized by a vitreous luster. It is brittle, and its Mohs hardness ranges from 4 to 4.5. The density is relatively high for a carbonate, approximately 4.03 g/cm³. ## Colors and Varieties Calcioancylite-(La) most often exhibits colors from pale pink to reddish-pink. No commercial or color varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – the dominance of calcium (Latin: *calcius*) and lanthanum (La) – and its relation to the structural ancylite group. It was first described by D.A. Mineev and co-workers in 1970 based on material from the Khibiny Massif in Russia, but its full characterization and approval by IMA occurred later. ## Uses Calcioancylite-(La) has no industrial applications. Its significance is purely scientific and as a collector's item, as a rare earth mineral.

Properties

Mohs hardness
4-0
Color
colourless to pale pinkish gray
Luster
Vitreous
Streak
white
Density
4.324
Cleavage
Good on {011}
Fracture
Irregular/Uneven
Transparency
Transparent,Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of calcioancylite-(La) is difficult without specialized tests. It can be preliminarily recognized by its characteristic pink color, form of small, sharply terminated crystals, and co-occurrence with other rare earth minerals in nepheline-syenite pegmatites. It reacts with acids. ## Distinguishing from Similar Minerals It can be confused with other minerals from the ancylite group, such as ancylite-(Ce) or calcioancylite-(Ce), from which differentiation is practically only possible using chemical analysis (EDS/WDS). Ewaldite or other rare carbonates may also have a similar appearance. ## Crystal Forms It forms columnar, prismatic crystals, often terminated by steep pyramid faces, which give them a sharp, spindle-like appearance. It occurs as single, grown crystals or small, radial aggregates.

Geological environment

## Genesis It is a low-temperature hydrothermal mineral. It forms in the late stages of crystallization of alkaline (nepheline-syenite) pegmatites and in carbonatites, where it crystallizes in rock cavities and fissures. ## Mineral Associations It often co-occurs with minerals such as: microcline, albite, aegirine, natrolite, calcite, burbankite, and other rare earth minerals, e.g., from the ancylite group. ## Localities The most important occurrences of this mineral worldwide include the type locality in the Khibiny Massif on the Kola Peninsula in Russia. It is also known from the Ilimaussaq alkaline complex in Greenland and the Poudrette quarry in Mont Saint-Hilaire, Quebec, Canada.

Rarity

Very rare

For collectors

## Quality Criteria Specimens most valued by collectors are those with well-formed, sharp crystals of intense pink color that contrast with the matrix minerals. Due to the small size of the crystals, their perfect form and lack of damage are crucial. Rich aggregates of several crystals are also highly prized. ## Popular Localities Specimens from Mont Saint-Hilaire, Canada, are considered among the best in the world, known for their sharp, well-formed crystals of beautiful color. Specimens from Russia and Greenland are also sought after, although they often have less aesthetic value.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to the small size of the crystals and their fragility, wet cleaning or ultrasonic cleaners are not recommended. ## What to Avoid The mineral is sensitive to acids, which cause it to dissolve rapidly with the release of carbon dioxide. Contact with any chemicals should be avoided. The crystals are brittle and susceptible to mechanical damage. ## Storage It is recommended to store specimens in sealed "micromount" boxes to protect them from dust and mechanical damage. Avoid areas of high humidity and direct exposure to sunlight.

External references

Sources

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