Nipeiite-(Ce)

Chemical formula: Ce<sup>3+</sup><sub>9</sub>Fe<sup>3+</sup>(SiO<sub>4</sub>)<sub>6</sub>[SiO<sub>3</sub>(OH)](OH)<sub>3</sub>

Nipeiite-(Ce) is an extremely rare mineral from the allanite group, characterized by a complex chemical composition with a dominance of cerium and iron.

## Characteristics Nipeiite-(Ce) is a mineral with a very complex chemical structure, belonging to the allanite group within the broader epidote supergroup. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2022. Its discovery took place in Japan. Due to its extreme rarity and microscopic crystal sizes, its full visual characterization is not well documented. It occurs as very fine, subhedral (partially formed) grains, usually not exceeding 0.2 mm in size. ## Physical Properties Nipeiite-(Ce) crystals exhibit a luster described as resinous to vitreous. They are brittle, and their Mohs hardness is approximately 6. The density calculated based on the chemical formula and unit cell parameters is 4.75 g/cm³. The mineral does not exhibit fluorescence. ## Colors and Varieties Observed grains of nipeiite-(Ce) are dark brown to black. Under a polarizing microscope in transmitted light, it exhibits pleochroism in shades from yellowish-brown to dark brown. No varieties have been distinguished. ## History and Name The mineral's name, nipeiite-(Ce), honors Professor Nipei Kouchi (born 1981), a Japanese geologist from Hokkaido University, for his contributions to petrology. The "(Ce)" suffix in the name indicates the dominance of cerium as a rare earth element in its crystal structure. The mineral was described by a research team, including Ritsuro Miyawaki, Koichi Momma, and others, based on material collected from the type locality. ## Uses Nipeiite-(Ce) has no commercial or industrial applications. Its significance is purely scientific and as a collector's item, being an extremely rare and newly discovered representative of the mineral world.

Properties

Mohs hardness
6
Luster
Resinous to Vitreous
Streak
Brown
Density
4.75
Cleavage
None
Fracture
Conchoidal
Transparency
Translucent to Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of nipeiite-(Ce) is impossible without advanced laboratory techniques. It requires chemical composition analysis using an electron microprobe (EDS/WDS) and structural analysis by X-ray diffraction (XRD). Visual characteristics, such as dark brown color and resinous luster, are non-specific and common to many minerals. ## Distinguishing from Similar Minerals Nipeiite-(Ce) is visually indistinguishable from other minerals of the allanite group, such as allanite-(Ce), ferriallanite-(Ce), or dissakisite-(Ce). All these minerals form similar, dark, fine grains in similar parageneses. The only way to differentiate them is through precise chemical and crystallographic analysis. ## Crystal Forms This mineral occurs as very small, subhedral (partially formed) grains, usually less than 0.2 mm in size, dispersed in the host rock.

Geological environment

## Genesis Nipeiite-(Ce) forms as a result of contact metamorphism processes. At the type locality, it was found in skarn formed at the contact of Paleozoic limestones with a Cretaceous granodiorite intrusion. Its presence is associated with metasomatic enrichment in rare earth elements and other specific components. ## Mineral Associations This mineral co-occurs with other minerals typical of a skarn environment. Its paragenesis includes andradite, hedenbergite, wollastonite, quartz, calcite, epidote, titanite, apatite, allanite-(Ce), and fluorite. ## Localities The only confirmed occurrence of nipeiite-(Ce) in the world is its type locality: the Doshinkubo skarn in Chichibu, Saitama Prefecture, Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, nipeiite-(Ce) is not evaluated according to typical aesthetic criteria, such as size or crystal form. The value of a specimen lies in its confirmed identity and the richness of the mineral association on the sample. The most valuable specimens are those where nipeiite-(Ce) grains are relatively numerous and clearly visible under a microscope, and their identity has been analytically confirmed. ## Popular Localities The only source of specimens is the type locality in Japan. Material from this location is extremely difficult to acquire and primarily goes to research institutions and specialized systematic mineral collections.

Care and storage

## Cleaning Due to its microscopic size and extreme rarity, nipeiite-(Ce) specimens are usually found within their host rock and should not be subjected to any cleaning treatments. Any attempt at mechanical or chemical cleaning risks irreversible destruction of the mineral. ## What to Avoid Avoid contact with any chemicals, ultrasonic cleaners, sudden temperature changes, and moisture. The specimen should be protected from dust and vibrations. ## Storage Specimens should be stored exclusively in specialized, stable containers (e.g., micromount type), away from light, in conditions of constant, low humidity and temperature. The safest place is a scientific institution's collection or an advanced collector with appropriate conditions.

Sources

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