Ferriakasakaite-(Ce)

Chemical formula: CaCe<sup>3+</sup>Fe<sup>3+</sup>AlMn<sup>2+</sup>(Si<sub>2</sub>O<sub>7</sub>)(SiO<sub>4</sub>)O(OH)

An extremely rare mineral from the epidote group, characterized by a complex chemical composition with the presence of cerium, iron, and manganese.

## Characteristics Ferriakasakait-(Ce) is a very rare mineral belonging to the epidote group. It occurs as subhedral (partially formed) grains up to 0.3 mm in size. It usually forms aggregates in association with other minerals. Its identification requires advanced analytical methods due to its small size and rarity. ## Physical Properties The mineral is characterized by a vitreous luster and is translucent. Its Mohs hardness is approximately 6.5, and its density is high, measured at 4.16 g/cm³. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties Ferriakasakait-(Ce) is dark brown to black. Due to its extreme rarity, no varieties have been distinguished. ## History and Name The mineral was first described in 2014 by D. Nishio-Hamane, T. Minakawa, H. Arakawa, and S. Ohnishi. Its name refers to its chemical composition – with dominant iron (ferri) and cerium (-Ce) – and honors Japanese mineralogist Masahide Akasaka (born 1950), a specialist in epidote group mineralogy. The type locality from which it originates is the Fuka mine in Okayama Prefecture, Japan.

Properties

Mohs hardness
6.5
Luster
Vitreous
Streak
Light brown
Density
4.16
Cleavage
Good on {001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of ferriakasakait-(Ce) is impossible without advanced laboratory techniques, such as X-ray microanalysis (EDS/WDS) and X-ray diffraction (XRD). In granular form, it is practically visually indistinguishable from other dark minerals of the epidote group, such as allanite or ferriallanite. ## Distinguishing from Similar Minerals It can be confused with other minerals of the epidote group, especially allanite-(Ce) and ferriallanite-(Ce). Definitive differentiation requires confirmation of the dominance of Fe³⁺ over Al in one of the structural sites and a specific ratio of individual elements, which is only possible through chemical analysis. ## Crystal Forms This mineral forms small, partially formed (subhedral) crystals with a prismatic habit, usually not exceeding 0.3 mm in length.

Geological environment

## Genesis Ferriakasakait-(Ce) forms as a result of metasomatic processes in contact zones (skarns) between carbonate rocks and magmatic intrusions. In its type locality (Fuka mine), it is a product of gehlenite alteration. ## Mineral Associations This mineral coexists with minerals such as wollastonite, gehlenite, vesuvianite, grossular, hubeite, andradite, hematite, calcite, and other minerals of the epidote group. ## Localities The only confirmed occurrence of ferriakasakait-(Ce) in the world is its type locality – the Fuka mine, near Takahashi city, Okayama Prefecture, on Honshu Island, Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" mineral, its collector value primarily depends on the confirmation of its identity by a reliable laboratory. The most valuable specimens are those where ferriakasakait-(Ce) grains are clearly visible, well-formed, and contrast with the surrounding host rock (matrix). The presence of rare associated minerals also increases the specimen's value. ## Popular Localities The only source of specimens is the Fuka mine in Japan, world-renowned for the occurrence of many rare skarn minerals.

Care and storage

## Cleaning Due to its extreme rarity and small crystal size, ferriakasakait-(Ce) specimens usually occur as grains embedded in the host rock. Mechanical cleaning is not recommended. If necessary, compressed air can be used to remove dust. ## What to Avoid Avoid contact with acids and other chemicals that could damage not only the mineral itself but also its associated minerals. Do not subject it to ultrasound or sudden temperature changes. ## Storage Specimens should be stored in stable conditions, in a closed "micromount" box, to protect them from dust and mechanical damage. Direct exposure to sunlight should be avoided, although there is no evidence of fading.

Sources

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