Bastnäsite-(Ce)

Chemical formula: Ce<sup>3+</sup>CO<sub>3</sub>F

Bastnäsite-(Ce) is a carbonate group mineral and an important ore of cerium and other rare earth metals, forming characteristic tabular crystals.

## Characteristics Bastnäsite-(Ce) is a cerium-dominant mineral of the bastnäsite group, belonging to the carbonate class. Its name refers to the dominant element in its structure – cerium. It typically forms tabular or short prismatic crystals with a hexagonal outline, often as granular, radial, or rosette-like aggregates. Specimens usually have a waxy or resinous luster, and their surfaces can be dull due to weathering. ## Physical Properties This mineral is characterized by a hardness of 4-4.5 on the Mohs scale, making it relatively soft. Its density is significant, approximately 4.9-5.2 g/cm³, which is noticeable even in small specimens. It is brittle, and its cleavage is imperfect or indistinct. The fracture is uneven. ## Colors and Varieties Bastnäsite-(Ce) most commonly occurs in colors ranging from yellow, through reddish-brown, to brown. Greenish or colorless specimens are rarer. No specific commercial or gemmological varieties are distinguished, and classification is based on the dominant rare earth element (e.g., bastnäsite-(La) with lanthanum, bastnäsite-(Y) with yttrium). ## History and Name The name "bastnäsite" comes from its discovery locality – the Bastnäs mine in Riddarhyttan, Västmanland region, Sweden. The mineral was first described by the Swedish chemist Wilhelm Hisinger in 1838. The suffix "-(Ce)" was later added by the International Mineralogical Association (IMA) to precisely specify the dominant rare earth element in this particular mineral of the group. ## Uses Bastnäsite-(Ce), along with monazite, is one of the world's most important sources for the extraction of cerium and other light rare earth elements (LREE). These elements have crucial applications in modern technologies, including the production of neodymium magnets, catalysts, specialized glass, phosphors, and in electronics.

Properties

Mohs hardness
4-4.5
Luster
Vitreous, Greasy, Pearly
Streak
White
Density
4.9-5.2
Cleavage
Imperfect/Fair on {0001}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Hexagonal

Diagnostic features

## Identification Bastnäsite-(Ce) can be identified by its characteristic tabular or short prismatic crystals with a hexagonal outline, waxy or resinous luster, and high density. An important diagnostic feature is its reaction with acids – it effervesces vigorously in contact with cold, dilute hydrochloric acid. It often exhibits weak radioactivity due to thorium impurities. ## Distinguishing from Similar Minerals Bastnäsite-(Ce) is sometimes confused with monazite, with which it often co-occurs. Monazite is usually harder (5-5.5) and crystallizes in the monoclinic system, forming crystals of a different shape. It is distinguished from calcite by its significantly higher density and different crystal form. Wulfenite, although similar in form (tabular crystals), is much denser and has a different chemical composition. ## Crystal Forms Bastnäsite-(Ce) crystals are typically simple, tabular, flattened parallel to the basal pinacoid {0001}, or short prismatic. They often form granular, rosette-like, radial aggregates, or massive concentrations. Crystals can be oriented parallel, forming stacks.

Geological environment

## Genesis Bastnäsite-(Ce) is a mineral of magmatic and hydrothermal origin. It forms mainly in carbonatites, which are magmatic carbonate rocks, as well as in alkaline pegmatites and syenites. It can also form in hydrothermal veins associated with alkaline rock intrusions. It also occurs in detrital form in alluvial deposits as a heavy mineral. ## Mineral Associations This mineral often co-occurs with other rare earth minerals and minerals typical of alkaline rocks and carbonatites. The most common associations include: allanite, cerite, monazite, fluorite, barite, calcite, dolomite, ankerite, and various minerals from the amphibole and pyroxene groups. ## Localities The most important localities globally for mining and collecting are the Bayan Obo deposit in China (the world's largest REE deposit), the Mountain Pass mine in California (USA), and the deposit in the Zagi Mountain mine in Pakistan, from which perfectly formed crystals originate. Other known occurrences include the Kola Peninsula in Russia, Burundi (Karonge), Madagascar, and the discovery site in Bastnäs, Sweden.

Rarity

Not very common

For collectors

## Quality Criteria The most prized by collectors are specimens with well-formed, sharp, and undamaged crystals with a distinct hexagonal outline. Crystals with intense, honey-yellow or reddish-brown color and good luster are highly valued. The attractiveness is enhanced by specimens where bastnäsite crystals grow on a contrasting rock matrix, for example, on white calcite or albite. Large, single crystals or aesthetic crystal groups (e.g., rosettes) fetch the highest prices. ## Popular Localities For collectors, specimens from Zagi Mountain in Pakistan are most sought after, known for their sharp, often partially transparent crystals of beautiful color, frequently in association with other rare minerals. Classic, though rarer, specimens are from Mountain Pass in California (USA) and historical samples from Bastnäs in Sweden.

Care and storage

## Cleaning Bastnäsite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Ultrasonic cleaners should not be used, as they can damage the brittle crystals. ## What to Avoid Bastnäsite is sensitive to acids, which cause it to effervesce vigorously and decompose. It should be protected from contact with household and laboratory chemicals. It is not particularly sensitive to light, but prolonged exposure to strong sunlight is not recommended. Sudden temperature changes should be avoided. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent scratching by harder minerals. Due to its relatively high density, even small specimens should be placed on a stable surface.

External references

Sources

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