Bastnäsite-(La)

Chemical formula: LaCO<sub>3</sub>F

Bastnäsite-(La) is a rare mineral from the rare earth group, a carbonate and fluoride of lanthanum, forming small, tabular crystals with a vitreous or resinous luster.

## Characteristics Bastnäsite-(La) is a mineral belonging to the bastnäsite group, in which lanthanum is the dominant rare earth element. It typically occurs as very small, hexagonal, tabular or prismatic crystals, often grouped into rosette aggregates. Specimens rarely reach sizes visible to the naked eye, and well-formed crystals are prized by collectors specializing in rare earth minerals. ## Physical Properties The mineral is characterized by a hardness of 4-4.5 on the Mohs scale. It has a vitreous to resinous luster on crystal faces and a greasy luster on fracture surfaces. It is brittle, and its density is approximately 4.95 g/cm³. It is transparent to translucent. ## Colors and Varieties Bastnäsite-(La) is usually colorless, white, yellowish, or reddish-brown. Its color depends on impurities of other elements. No named commercial or colored varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition, with lanthanum (La) as the dominant rare earth element, and to its association with the bastnäsite group. It was formally described as a distinct mineral species in 1964 by Akira Kato and Kin-ichi Sakurai, based on material from the Suishoyama mine in Fukushima Prefecture, Japan. The group name originates from the Swedish Bastnäs mine, where bastnäsite was first identified. ## Uses Along with other minerals from this group, bastnäsite-(La) is a potential source of lanthanum and other rare earth elements, which are crucial in modern technologies such as the production of catalysts, magnets, and specialized optics. Due to its rarity and small crystal size, its importance as a raw material is less than that of the more common bastnäsite-(Ce).

Properties

Mohs hardness
4-4.5
Luster
Vitreous to resinous
Streak
White
Density
4.95
Cleavage
Good on {0001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Hexagonal

Diagnostic features

## Identification A characteristic feature is its occurrence in the form of small, hexagonal, tabular crystals, often in association with other rare earth minerals. Reaction with hydrochloric acid (violent effervescence) is a strong diagnostic indicator for carbonates, including bastnäsite. However, identification requires advanced analytical methods (e.g., EDS/WDS) to confirm the dominance of lanthanum over other rare earth elements. ## Distinguishing from Similar Minerals Bastnäsite-(La) is visually indistinguishable from other minerals of the bastnäsite group, such as bastnäsite-(Ce) or bastnäsite-(Y). It can be confused with other fine-grained, light-colored minerals, e.g., some micas or apatite, from which it is distinguished by its higher density and reaction with acids. ## Crystal Forms It forms thin, tabular crystals with a hexagonal outline. It also occurs as short prisms. Crystals often form radial or rosette aggregates, as well as granular masses in the host rock.

Geological environment

## Genesis Bastnäsite-(La) forms in the late stages of hydrothermal processes associated with intrusions of alkaline rocks, such as carbonatites and syenites. It can also form as a result of metasomatism in sedimentary or metamorphic rocks, under the influence of solutions rich in rare earth elements. ## Mineral Associations It co-occurs with other rare earth minerals, such as monazite, allanite, cerite, as well as fluorite, barite, quartz, and calcite. In carbonatites, it is often accompanied by pyrochlore and niobite. ## Localities Key localities worldwide include: Suishoyama mine, Fukushima Prefecture, Japan (type locality); carbonatite complexes on the Kola Peninsula in Russia (e.g., Khibiny Massif); deposits in Mountain Pass, California, USA; as well as occurrences in Norway and Sweden.

Rarity

Rare

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, sharp crystals with a distinct hexagonal outline, even if they are small. Rich aggregates of crystals on a contrasting rock matrix are also highly prized. Purity and intensity of color (especially yellow and brown hues) can increase the value of a specimen, although in the case of this mineral, crystal form is more important. ## Popular Localities Specimens from the type locality, the Suishoyama mine in Japan, are of particular value to collectors. Well-crystallized samples from Russian alkaline massifs on the Kola Peninsula are also highly regarded.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Distilled water is permissible, but prolonged soaking should be avoided. Always dry the specimen thoroughly after cleaning. ## What to Avoid The mineral is sensitive to acids, which cause it to effervesce violently and decompose. Contact with household chemicals and acids should be avoided. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to protect them from mechanical damage and scratching by harder minerals. They should be protected from dust and moisture.

External references

Sources

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