Vanadoakasakaite-(Ce)

Chemical formula: CaCe₃+(V₃+AlMn₂+)(Si₂O₇)(SiO₄)O(OH)

Vanadoakasakaite-(Ce) is a very rare mineral from the allanite group, a calcium, cerium, and vanadium silicate, found in Japan.

## Characteristics Vanadoakasakaite-(Ce) is an extremely rare mineral belonging to the allanite group. It occurs as very fine, subhedral (partially formed) grains, usually not exceeding 0.1 mm in size. Due to its size, its macroscopic features are difficult to observe without specialized equipment. This mineral is embedded in the host rock, forming small aggregates. ## Physical Properties The mineral is characterized by a vitreous luster. It is opaque. Its Mohs hardness is 6. The density calculated based on the chemical formula and unit cell parameters is 4.16 g/cm³. ## Colors and Varieties The observed grains of vanadoakasakaite-(Ce) are black with a brownish tint. In transmitted light under a polarizing microscope, it exhibits strong pleochroism in shades from reddish-brown to pale yellow. No varieties of this mineral have been distinguished. ## History and Name Vanadoakasakaite-(Ce) was officially recognized by the International Mineralogical Association (IMA) in 2014 under number IMA2014-062. Its name refers to its chemical composition – the presence of vanadium as the dominant trivalent element at one of the structural sites – and its relationship to akasakaite-(Ce). The -(Ce) suffix indicates cerium as the dominant rare-earth element. The name akasakaite comes from the discovery locality – the Akasaka quarry in Japan. The mineral was described by a Japanese research team, including Daisuke Nishio-Hamane.

Properties

Mohs hardness: 6
Luster: Vitreous
Streak: Brown
Density: 4.16
Cleavage: Good on {001}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of vanadoakasakaite-(Ce) is only possible using advanced laboratory methods, such as X-ray microanalysis (EDS/WDS) to determine chemical composition and X-ray diffraction (XRD) for crystal structure analysis. Visual features, such as black color, brownish tint, and strong pleochroism in thin sections, are helpful but insufficient for definitive identification. ## Distinguishing from Similar Minerals The mineral is almost impossible to distinguish from other black minerals of the allanite group (e.g., allanite-(Ce), vanadoallanite-(Ce), akasakaite-(Ce)) without chemical analysis. The key is to confirm the dominance of vanadium (V³⁺) over aluminum and iron (Fe³⁺) at a specific site in the crystal structure. ## Crystal Forms Vanadoakasakaite-(Ce) forms very small, poorly developed, subhedral grains, occurring as inclusions in other minerals or in the rock matrix.

Geological environment

## Genesis Vanadoakasakaite-(Ce) forms as a result of metamorphic processes. At the type locality (Akasaka quarry), it occurs in limestone subjected to contact metamorphism by granite intrusion. This is an environment rich in calcium and rare-earth elements. ## Mineral Associations This mineral coexists with minerals such as calcite, hornblende, titanite, zircon, apatite, molybdenite, as well as other minerals from the epidote and allanite groups, including akasakaite-(Ce). ## Localities The only confirmed occurrence of vanadoakasakaite-(Ce) in the world is its type locality – the Akasaka quarry, in Ōgaki city, Gifu Prefecture, Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria From a collector's perspective, vanadoakasakaite-(Ce) is typically a systematic mineral, valued for its mere presence in a collection rather than its aesthetic qualities. Specimens where the mineral has been identified and analytically documented are the only valuable ones. The size of the host rock specimen is not of great importance; the confirmed presence of the mineral is what matters. ## Popular Localities The only source of specimens is the Akasaka quarry in Japan. Due to its extreme rarity, specimens are practically unavailable on the open commercial market and are mainly found in institutional and specialized collections.

Care and storage

## Cleaning Due to the extreme rarity and microscopic size of the crystals embedded in the host rock, specimens of vanadoakasakaite-(Ce) are not subject to standard cleaning. Any intervention should be performed exclusively in laboratory conditions by specialists. ## What to Avoid All chemical and mechanical cleaning methods, including ultrasonics, which could damage or destroy the microscopic mineral grains and the surrounding rock, should be avoided. ## Storage Specimens should be stored in stable conditions, in specialized containers (so-called micromounts), protecting them from dust, moisture, and mechanical damage. Exposure to direct sunlight and extreme temperatures should be avoided.

Sources

IMA Mineral List (CNMNC)