Håleniusite-(Ce)

Chemical formula: Ce³⁺OF

Håleniusite-(Ce) is a rare cerium oxide fluoride, forming small, hexagonal crystals of yellow color and resinous luster.

## Characteristics Håleniusite-(Ce) is a mineral belonging to the halide group. It occurs as very small, hexagonal, tabular or prismatic crystals, rarely exceeding 0.2 mm. It also forms aggregates and rosettes. It is a transparent mineral with a characteristic, light yellow to yellowish-brown color. ## Physical Properties This mineral is characterized by a resinous luster. Its Mohs hardness is approximately 4.5, and its density is high at 6.26 g/cm³. It is brittle and exhibits an uneven fracture. ## Colors and Varieties Observed colors are light yellow, yellow to yellowish-brown. No specific varieties of this mineral have been distinguished. ## History and Name The mineral is named in honor of Ulf Hålenius (born 1951), professor of mineralogy and former head of the mineralogy department at the Swedish Museum of Natural History in Stockholm. It was approved as a new mineral by the IMA in 2002. The type locality is the Östanmossa mine in Norberg, Sweden. ## Applications Due to its rarity and microscopic crystal sizes, Håleniusite-(Ce) has no industrial application and is solely an object of interest for collectors specializing in rare minerals and for scientists.

Properties

Mohs hardness
4.5
Color
cream
Luster
Resinous
Streak
white
Density
5.890
Cleavage
Good on {0001}
Fracture
Uneven
Transparency
Opaque
Crystal system
Isometric

Diagnostic features

## Identification In practice, the identification of Håleniusite-(Ce) relies on its characteristic occurrence environment, associated minerals, and specific form. Small, hexagonal, tabular crystals of yellow color and resinous luster are typical. However, definitive confirmation requires advanced analytical methods, such as energy-dispersive X-ray spectroscopy (EDS) or X-ray diffraction (XRD), due to its similarity to other rare earth minerals. ## Distinguishing from Similar Minerals It can be confused with other minerals from the bastnäsite group or other rare oxide fluorides. Visual distinction is practically impossible without chemical analysis, which would show the presence of cerium, oxygen, and fluorine in appropriate proportions. ## Crystal Forms It forms hexagonal, tabular or short prismatic crystals. It often occurs as radial aggregates or rosettes composed of many small crystals.

Geological environment

## Genesis It is a hydrothermal mineral, forming in the late stages of crystallization in iron- and manganese-rich skarn deposits. It forms in fractures and small rock cavities. ## Mineral Associations It most commonly co-occurs with hematite, magnetite, fluorite, barite, törnebohmit-(Ce), bastnäsite-(Ce), cerianite-(Ce), and minerals from the allanite group. ## Localities The most important and type locality is the historic Östanmossa iron ore mine in the municipality of Norberg, in the Västmanland region of Sweden. This is the only confirmed and well-documented location for this mineral in the world.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of Håleniusite-(Ce) specimens is primarily assessed based on the abundance and development of crystals on the rock matrix. The most desirable specimens are those with clearly visible, sharp, well-formed crystals or rich aggregates thereof. A contrasting matrix, for example with hematite, enhances visual appeal. Due to the microscopic nature of the mineral, even small but well-defined crystals are highly valued. ## Popular Localities The only source of collector specimens is the Östanmossa mine in Sweden. All specimens available on the market originate from this single locality.

Care and storage

## Cleaning Due to the extreme rarity and small size of the crystals, mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used to remove dust. Avoid contact with water and chemicals. ## What to Avoid Avoid contact with acids, which can damage the mineral. Crystals are brittle, so protect them from impacts and vibrations. Do not subject it to ultrasonic cleaning. ## Storage Håleniusite-(Ce) specimens are typically microscopic and stored in specialized "micromount" boxes. They should be kept in a stable environment, away from dust, moisture, and extreme temperatures, to prevent damage.

External references

Sources

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