Ferriperbøeite-(Ce)

Chemical formula: (CaCe<sup>3+</sup><sub>3</sub>)(Fe<sup>3+</sup>Al<sub>2</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>

Ferriperbøeite-(Ce) is a very rare mineral from the epidote group, characterized by a complex chemical composition with dominant cerium.

## Characteristics Ferriperbøeite-(Ce) is a mineral belonging to the epidote group. It occurs as subhedral (poorly formed) grains up to 0.5 mm in size, forming aggregates within the host rock. Its appearance is inconspicuous, and identification requires advanced analytical methods. ## Physical Properties This mineral is characterized by a vitreous luster. It is brittle, and its Mohs hardness is 6. The density calculated based on the chemical formula and unit cell parameters is 4.31 g/cm³. ## Colors and Varieties Ferriperbøeite-(Ce) is black in color, and in transmitted light under a microscope, it exhibits strong pleochroism in shades from dark greenish-brown to light brown. No varieties have been distinguished. ## History and Name The mineral's name refers to its chemical composition - the dominance of iron (ferri) and cerium (-Ce) and its structural relationship to perbøeite. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2013 (IMA number 2013-058). It was described by G. Giester et al. in 2014 based on material from the type locality in Norway.

Properties

Mohs hardness
6
Luster
Vitreous
Streak
Light brown
Density
4.31
Cleavage
Good on {001}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Macroscopic identification of ferriperbøeite-(Ce) is impossible. Identification requires specialized analytical techniques, such as X-ray microanalysis (EDS/WDS) to determine chemical composition and X-ray diffraction (XRD) to confirm crystal structure. ## Distinguishing from Similar Minerals It can be confused with other black minerals from the epidote group, such as allanite-(Ce) or ferriallanite-(Ce). Differentiation is possible only on the basis of precise chemical analysis, which will show specific proportions of iron (Fe³⁺ and Fe²⁺), aluminum, and cerium. ## Crystal Forms This mineral forms poorly developed, subhedral grains that occur as aggregates within the rock. No well-formed, freestanding crystals have been observed.

Geological environment

## Genesis Ferriperbøeite-(Ce) forms under conditions of regional metamorphism in the amphibolite facies. It occurs in gneissic rocks that have been subjected to high pressures and temperatures. ## Mineral Associations This mineral coexists with quartz, microcline, biotite, plagioclase, titanite, allanite-(Ce), apatite, zircon, monazite-(Ce), and epidote. ## Localities The only confirmed occurrence (type locality) of ferriperbøeite-(Ce) is a rock outcrop in Heftetjern, in the municipality of Tørdal, Telemark region, Norway.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its extreme rarity and occurrence only as microscopic grains, the only criterion of value for collectors is the mere confirmation of the mineral's presence on a rock fragment from the type locality. Specimens are of purely scientific and systematic interest. ## Popular Localities The only source of material is the type locality in Heftetjern, Norway. Specimens are practically unavailable on the commercial market and are mainly found in the collections of scientific institutions.

Care and storage

## Cleaning Due to its extreme rarity and small grain size, specimens containing ferriperbøeite-(Ce) are practically not subject to cleaning. Any attempts at mechanical or chemical intervention can irreversibly damage or destroy the mineral. Only dust removal using compressed air is recommended. ## What to Avoid Avoid contact with any chemicals, acids, and detergents. The mineral is brittle, so it should be protected from impacts, vibrations, and sudden temperature changes. ## Storage Specimens should be stored under stable conditions, in sealed "micromount" boxes, protected from dust and mechanical damage. Avoid exposure to direct sunlight and moisture.

Sources

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