Vielleaureite-(Ce)

Chemical formula: Mn²⁺Ce³⁺(MgAlMn²⁺)(Si₂O₇)(SiO₄)F(OH)

Vielleaureite-(Ce) is a very rare mineral from the epidote group, discovered in the French Pyrenees, distinguished by its complex chemical composition with manganese and cerium.

## Characteristics Vielleaureite-(Ce) is a very rare mineral belonging to the epidote group. It forms small, prismatic crystals up to 0.5 mm long, which most often occur as radial or fibrous aggregates. Its appearance is inconspicuous, and identification requires advanced analytical methods due to the small size of the crystals and its rarity. ## Physical Properties Vielleaureite-(Ce) crystals exhibit a vitreous luster. The mineral is brittle. Its Mohs hardness is approximately 6, and its density is estimated at 4.15 g/cm³. It is an optically biaxial positive mineral. ## Colors and Varieties This mineral is characterized by a color ranging from reddish-brown to dark brown. No color varieties or commercial forms are known. ## History and Name The mineral's name comes from its discovery locality – the Vieille-Aure mine in the Aure valley, Hautes-Pyrénées department, France. The "-(Ce)" suffix indicates the dominant rare earth element in its composition, which is cerium. The mineral was approved by the International Mineralogical Association (IMA) in 2002 under number IMA2002-038. It was described by P. Lapeyre, F. Fontan, F. Pillard, P. de Parseval, R. Permingeat, and P. Orliac. ## Uses Vielleaureite-(Ce) has no industrial applications. Due to its extreme rarity and microscopic crystal size, it is of purely scientific interest and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness
6-0
Color
dark reddish brown
Luster
Vitreous
Streak
reddish brown
Density
4.33
Cleavage
Good on {100}
Fracture
Irregular/Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of Vielleaureite-(Ce) is impossible without advanced analytical techniques such as energy-dispersive spectroscopy (EDS/WDS) or X-ray diffraction (XRD). Preliminary field identification is practically unfeasible. In a collection, it might be suspected based on its reddish-brown color, radial aggregates, and confirmed locality (Vieille-Aure mine). ## Distinguishing from Similar Minerals This mineral can be confused with other reddish-brown minerals from the epidote group, such as piemontite or dollaseite-(Ce), which occur in similar parageneses. Final distinction requires chemical analysis to confirm its unique composition, particularly the content of fluorine, magnesium, and the dominance of cerium. ## Crystal Forms Vielleaureite-(Ce) forms elongated, prismatic crystals that rarely occur individually. Most often, it forms radial or fibrous aggregates, as well as granular clusters within the host rock.

Geological environment

## Genesis Vielleaureite-(Ce) forms as a result of metamorphic and metasomatic processes in manganese-rich rocks. In its type locality (Vieille-Aure mine), it occurs in veins cutting Ordovician volcanics and sediments that underwent contact and regional metamorphism during the Variscan orogeny. ## Mineral Associations This mineral co-occurs with other manganese and rare earth element minerals. In its type locality, it was found in association with quartz, tephroite, piemontite, dollaseite-(Ce), manganese oxides, fluorite, barite, and calcite. ## Localities The only confirmed and described occurrence of Vielleaureite-(Ce) in the world is its type locality: the Vieille-Aure mine in the Aure valley, Hautes-Pyrénées department, Occitanie region, France.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a Vielleaureite-(Ce) specimen is primarily assessed based on the richness and visibility of aggregates on the rock matrix. Since the crystals are microscopic, specimens with clearly visible, well-formed radial clusters are most desirable. The color contrast of the mineral with the surrounding rock also enhances its attractiveness. The certainty of identification, confirmed by analysis, is also crucial. ## Popular Localities The only source of Vielleaureite-(Ce) specimens is the Vieille-Aure mine in France. This is a historic manganese mine, and the material for research comes from old dumps. Specimens from this locality are extremely difficult to acquire and represent a rarity in any collection specializing in systematics or rare minerals.

Care and storage

## Cleaning Due to its extreme rarity and brittleness, Vielleaureite-(Ce) specimens should only be cleaned if absolutely necessary. It is recommended to use compressed air to remove dust. Any contact with water or chemicals is discouraged without consulting an expert. ## What to Avoid Avoid ultrasonic cleaners, chemical agents, acids, and sudden temperature changes. The mineral is brittle, so protect it from impacts and vibrations. Do not expose it to direct sunlight, although its stability in light has not been fully investigated. ## Storage Specimens should be stored in stable conditions, preferably in a sealed "micromount" box, to protect them from dust, mechanical damage, and humidity. Display should occur under controlled conditions, away from sources of vibration and direct light.

External references

Sources

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