Perbøeite-(La)

Chemical formula: (CaLa<sub>3</sub>)(Al<sub>3</sub>Fe<sup>2+</sup>)[Si<sub>2</sub>O<sub>7</sub>][SiO<sub>4</sub>]<sub>3</sub>O(OH)<sub>2</sub>

Perbøeite-(La) is a very rare mineral from the epidote group, characterized by a complex chemical composition with dominant lanthanum.

## Characteristics Perbøeite-(La) is a mineral belonging to the epidote group. It occurs as subhedral (poorly formed) grains up to 200 micrometers in size, forming aggregates within the host rock. It is a dark brown to almost black, opaque mineral with a vitreous luster. ## Physical Properties Due to the small size of the grains, most physical properties have not been precisely determined. Hardness is estimated to be around 6-7 on the Mohs scale, similar to other minerals in this group. The density calculated based on the formula and unit cell parameters is 4.55 g/cm³. ## Colors and Varieties This mineral is dark brown to black. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name honors the Norwegian mineral collector Perbøe Knudtzon (1880–1936). The -(La) suffix indicates lanthanum as the dominant rare earth element in its composition. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2011 (number 2011-066). It was described by N.V. Chukanov et al. in 2013. ## Applications Perbøeite-(La) has no industrial applications and is solely an object of scientific and collecting interest for specialists accumulating rare minerals and microminerals.

Properties

Mohs hardness
6-7
Luster
Vitreous
Streak
Light brown
Density
4.55
Cleavage
Good on {001}
Fracture
Uneven
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of perbøeite-(La) is impossible without advanced analytical methods. This requires chemical analysis (e.g., electron microprobe - EDS/WDS) to confirm the complex composition with dominant lanthanum, and X-ray diffraction to determine the crystal structure. Visually, it is simply a dark, vitreous grain in the rock. ## Distinguishing from Similar Minerals It can be confused with other minerals from the epidote group, such as allanite, dollaseite, or ferriallanite, as well as other dark rock-forming minerals. Definitive distinction is only possible based on detailed laboratory analyses. ## Crystal Forms It forms poorly developed, subhedral grains, which may occur as small aggregates.

Geological environment

## Genesis Perbøeite-(La) forms as a result of metasomatic processes within nepheline syenites. In its type locality (Mount Eveslogchorr), it occurs in hydrothermal veins cutting foyaite (a variety of nepheline syenite). ## Mineral Associations This mineral is associated with minerals such as microcline, nepheline, aegirine, eudialyte, lorenzenite, lamprophyllite, rinkite, fluorite, as well as other minerals from the epidote group. ## Localities The only confirmed occurrence of perbøeite-(La) in the world is its type locality – Mount Eveslogchorr in the Khibiny Massif on the Kola Peninsula, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria As a micromineral, perbøeite-(La) is not evaluated according to typical criteria such as color or clarity. Specimens where the mineral grains are as well-formed as possible and clearly visible against the host rock are of the highest value. Crucial are also correct analytical identification and the richness of associated minerals on the sample. ## Popular Localities The only source of specimens is the Khibiny Massif on the Kola Peninsula, Russia.

Care and storage

## Cleaning Specimens of this mineral are typically small grains embedded in rock. Cleaning is not recommended to avoid damaging the delicate crystals and their surroundings. If necessary, compressed air can be used to remove dust. ## What to Avoid Avoid contact with chemicals, acids, and ultrasonic cleaners, which can damage both the mineral itself and the host rock. ## Storage Micromount specimens of perbøeite-(La) should be stored in specialized boxes (so-called micromount boxes), protecting them from dust, moisture, and mechanical damage.

Sources

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