Bastnasite-series

Chemical formula: [Ce,La,Nd,Y][CO<sub>₃</sub>][F,OH]

A group of rare-earth carbonate-fluoride minerals, being the main industrial source of cerium, lanthanum, and other lanthanides.

## Characteristics Bastnäsite is not a single mineral, but the name of a series of three carbonate-fluoride minerals: bastnäsite-(Ce), bastnäsite-(La), and bastnäsite-(Y), depending on the dominant rare-earth element. It typically forms tabular or short-prismatic crystals with a hexagonal outline, often grouped into rosettes or granular and massive aggregates. Specimens are usually opaque to translucent, with a waxy or resinous luster, and vitreous on crystal faces. It is a relatively heavy and brittle mineral. ## Physical Properties Its Mohs hardness ranges from 4 to 4.5, making it a relatively soft mineral. The density is high, ranging from 4.9 to 5.2 g/cm³, which is characteristic of minerals containing rare-earth elements. Minerals from this series exhibit weak cleavage. ## Colors and Varieties The most common colors are yellow, reddish-brown, waxy-yellow, and honey-brown. Less frequently, it can be greenish or gray. Individual minerals of the series (with the -Ce, -La, -Y suffix) are not considered distinct varieties in a collector's sense, and their differentiation requires advanced chemical analysis. ## History and Name The name comes from its discovery location – the Bastnäs mine in Riddarhyttan, Västmanland, Sweden. It was named in 1838 by the Swedish chemist Wilhelm Hisinger. Initially, it was described as a single mineral; only later, with the development of analytical techniques, was it separated into a series depending on the dominant lanthanide. ## Applications The bastnäsite series, alongside monazite, is the world's most important source of rare-earth elements, especially cerium and lanthanum. These elements are crucial in modern technologies, including the production of strong magnets, catalysts, specialized glass, electronics, and in the petroleum industry.

Properties

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

Diagnostic features

## Identification Bastnäsite can be identified by its characteristic, hexagonal, tabular crystals, high density (the specimen feels heavier than it looks), resinous or waxy luster, and colors ranging from yellow to reddish-brown. A key diagnostic feature is its violent reaction with a drop of dilute hydrochloric acid (it effervesces). ## Distinguishing from Similar Minerals It can be confused with monazite, which often co-occurs and has similar colors, but typically forms crystals of a different shape (wedge-shaped, monoclinic) and does not react with acid. Parisite is visually and chemically very similar but has a more complex structure and often forms sharper, more elongated crystals; differentiation is often impossible without X-ray diffraction (XRD) analysis. Other minerals with a similar appearance, such as some sphalerites or epidotes, differ in hardness, density, and lack of reaction with acid. ## Crystal Forms Most commonly, it occurs as thin to thick tabular crystals with a hexagonal outline. Crystals can be terminated by flat basal faces or pyramids. It often forms granular, massive aggregates, as well as radial or fan-shaped clusters.

Geological environment

## Genesis Bastnäsite is a mineral of magmatic and hydrothermal origin. It crystallizes mainly in the late stages of cooling of magmas rich in rare-earth elements and alkalis, forming deposits in carbonatites, fenites, and syenite pegmatites. It can also form as a result of hydrothermal processes in veins and metasomatic zones, where REE-rich fluids react with carbonate rocks. ## Mineral Associations It often co-occurs with other rare-earth minerals such as monazite, allanite, cerite, as well as with fluorite, barite, calcite, dolomite, and various minerals from the amphibole and pyroxene groups. ## Localities The most important and largest industrial deposits in the world are Mountain Pass in California (USA) and Bayan Obo in Inner Mongolia (China). Other significant localities include the Kola Peninsula (Russia), the Karonge area (Burundi), as well as numerous occurrences in pegmatites and carbonatites in Norway, Sweden (type locality - Bastnäs), Pakistan (Kashmir mountains), Afghanistan, and Canada (Quebec).

Rarity

Not very common

For collectors

## Quality Criteria Specimens with well-formed, sharp, and clearly defined crystals are most valued by collectors, especially those with a tabular and hexagonal habit. Crystals with good transparency and a vibrant, honey-yellow or reddish-brown color are highly prized. The attractiveness of a specimen is enhanced by its placement on a contrasting matrix, e.g., on white calcite or fluorite. Large, single crystals or aesthetic groups (e.g., rosettes) fetch higher prices. ## Popular Localities Specimens of the best crystalline quality, often sharp and partially transparent, come from the mountains of Pakistan (around Zagi Mountain). Classic, historical specimens originate from Sweden (Bastnäs). Large, though often less aesthetic crystals, are found in Mountain Pass, USA.

Care and storage

## Cleaning 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 be avoided, as they can damage brittle crystals. ## What to Avoid Bastnäsite is sensitive to acids, which cause it to effervesce violently 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. ## Storage Due to its relatively low hardness, bastnäsite specimens should be stored separately in padded boxes to prevent scratching by harder minerals (e.g., quartz). It does not require special humidity conditions.

Sources

IMA Mineral List (CNMNC)