Hydroxylbastnäsite-(Ce)

Chemical formula: Ce<sup>3+</sup>CO<sub>3</sub>(OH)

Hydroxylbastnäsite-(Ce) is a rare mineral from the carbonate group, characterized by its occurrence as small, hexagonal crystals and aggregates.

## Characteristics Hydroxylbastnäsite-(Ce) is a mineral belonging to the bastnäsite group, being a hydroxyl analog of bastnäsite-(Ce). It typically forms very small, hexagonal, tabular or prismatic crystals. It also occurs in the form of rosette-like, spherulitic (spherical) aggregates, or as coatings and efflorescences on other minerals. Due to the small size of the crystals, its visual features are often difficult to observe without magnification. ## Physical Properties Crystals exhibit a vitreous to greasy luster. The mineral is relatively soft, with a Mohs hardness of approximately 4. It is a fairly dense mineral, which is typical for minerals containing rare earth elements. It is transparent to translucent. ## Colors and Varieties Hydroxylbastnäsite-(Ce) occurs in various colors; most often it is waxy yellow, light yellow, yellowish-brown, reddish-brown, as well as gray or colorless. No named varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – the presence of a hydroxyl group (OH) – and its relation to the much more common bastnäsite. The -(Ce) suffix indicates that cerium is the dominant rare earth element in its structure. It was first described by A.A. Kiriukov and co-workers in 1964. ## Uses Due to its rarity and small occurrences, hydroxylbastnäsite-(Ce) has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or rare earth minerals.

Properties

Mohs hardness
4
Luster
Vitreous to greasy
Streak
White to light gray
Density
4.7-4.8
Cleavage
Good on {0001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Hexagonal

Diagnostic features

## Identification Identification of hydroxylbastnäsite-(Ce) is extremely difficult without advanced analytical methods. Visually, it is practically impossible to distinguish from other minerals of the bastnäsite group (bastnäsite-(Ce), torybastnäsite) and from some similar carbonates and phosphates. The characteristic hexagonal crystal habit and co-occurrence with other rare earth minerals can be a clue, but certain identification requires chemical analysis (EDS) and/or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with bastnäsite-(Ce), parisite, cordylite, and also monazite. Bastnäsite-(Ce) is its fluorinated analog and often co-occurs in the same parageneses, making differentiation impossible without laboratory tests. Monazite has similar colors but crystallizes in the monoclinic system. ## Crystal Forms Most often, it forms small, tabular or short-prismatic crystals with a hexagonal outline. They frequently occur as radial or rosette-like aggregates, as well as spherical spherulites. They can form coatings on other minerals.

Geological environment

## Genesis Hydroxylbastnäsite-(Ce) is a secondary mineral, formed in the weathering (oxidation) zones of carbonatite deposits, alkaline pegmatites, and other rocks rich in rare earth elements. It forms as a result of hydrothermal alteration or weathering of primary rare earth minerals, such as allanite, cerite, or tysonite-(Ce). ## Mineral Associations It often co-occurs with other rare earth minerals, such as bastnäsite-(Ce), cerite-(Ce), allanite-(Ce), tengerite-(Y), lokkaite-(Y), as well as fluorite, barite, calcite, and quartz. ## Localities Important localities worldwide include those in carbonatites on the Kola Peninsula in Russia (Vuoriyarvi). This mineral has also been found in the USA (Mountain Pass mine in California; Iron Hill in Colorado), Canada (Mont Saint-Hilaire, Quebec), Sweden (Bastnäs), and Burundi.

Rarity

Rare

For collectors

## Quality Criteria Specimens with well-formed, sharp crystals, even if small, are most valued by collectors. The intensity and attractiveness of the color (e.g., vivid shades of yellow) are important. Rich crystal aggregates or aesthetic associations with other, contrasting minerals are also highly prized. Due to the small size of the crystals, many specimens are "micromounts," where the perfection of form visible under a microscope is key. ## Popular Localities Specimens from classic localities, such as the Kola Peninsula in Russia or Mont Saint-Hilaire in Canada, are particularly sought after due to the quality of the crystals and the historical significance of these places.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to possible reactivity with acids, all chemical cleaning agents should be avoided. If liquid is necessary, distilled water is recommended, followed by very gentle drying. ## What to Avoid Contact with acids, which can damage or completely dissolve the mineral, must be absolutely avoided. It should not be heated or subjected to ultrasound. Prolonged exposure to strong sunlight is not advisable. ## Storage Hydroxylbastnäsite-(Ce) specimens, often occurring as small and fragile crystals, should be stored in sealed "micromount" boxes, which protect them from mechanical damage and dust. They should be kept away from minerals that could scratch them.

Sources

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