Vanadoakasakaite-(La)

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

An extremely rare mineral from the epidote group, discovered in Japan, with a complex chemical composition containing lanthanum and vanadium.

## Characteristics Vanadoakasakaite-(La) is a very rare mineral belonging to the allanite subgroup within the epidote group. It is a lanthanum and vanadium (V³⁺) analogue of akasakaite-(La). It occurs as subhedral (poorly formed) grains up to 0.3 mm in size, forming aggregates within other minerals. It is opaque, black in color, and has a resinous luster. ## Physical Properties The mineral is characterized by a Mohs hardness of approximately 6. It has a resinous luster and is brittle. Its density, calculated based on the chemical formula and unit cell parameters, is 4.14 g/cm³. ## Colors and Varieties Vanadoakasakaite-(La) is black. Due to its extreme rarity, no varieties have been distinguished. ## History and Name The mineral's name refers to its chemical composition – the dominance of vanadium (V³⁺) and lanthanum (La) – and its structural relationship to akasakaite-(La). It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2014 (IMA number IMA2014-063). It was described by Japanese mineralogists: Daisuke Nishio-Hamane, Minoru Taniguchi, Koichi Momma, Tetsuo Minakawa, and Masayuki Ohnishi in 2017. ## Applications Due to its extreme rarity and microscopic size, Vanadoakasakaite-(La) has no practical applications. It is of purely scientific significance and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness: 6
Luster: Resinous
Streak: Grayish black
Density: 4.14
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of Vanadoakasakaite-(La) is impossible without advanced analytical techniques. It requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm the presence and dominance of lanthanum, calcium, vanadium, aluminum, and manganese. Structural analysis, e.g., by X-ray diffraction (XRD), is also necessary. ## Distinguishing from Similar Minerals The mineral is visually indistinguishable from other black, microscopic minerals of the epidote group, such as allanite-(La), allanite-(Ce), ferriallanite-(La), or akasakaite-(La). Differentiation is based solely on precise chemical analysis, particularly on determining which rare earth element (La, Ce) and which transition metal (V, Fe, Mn) dominates in specific positions within the crystal structure. ## Crystal Forms It has only been observed as poorly formed, irregular grains up to 0.3 mm in size, often intergrown with other minerals.

Geological environment

## Genesis Vanadoakasakaite-(La) forms as a result of metamorphic processes. It was discovered in manganese ore deposits embedded in a Jurassic accretionary complex that underwent metamorphism under greenschist facies conditions. ## Mineral Associations This mineral coexists with minerals such as quartz, rhodochrosite, tephroite, albite, celsian, hyalophane, aegirine, sérandite, namansilite, natronamblygonite, wallisite, and stronalsite. ## Localities The only confirmed worldwide occurrence (type locality) is the Shobu mine, located in Mie Prefecture, Kinki region, on Honshu Island, Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a Vanadoakasakaite-(La) specimen is determined solely by its scientific and documentary value. Since the mineral is microscopic, collector specimens are typically fragments of the host rock (matrix) with rich aggregates of this mineral's grains. Specimens whose identity has been confirmed by chemical analysis (co-type material) are most highly valued. The aesthetics of the specimen itself are of secondary importance. ## Popular Localities The only source of specimens is the type locality – the Shobu mine in Japan. Material from this mine is extremely difficult to obtain.

Care and storage

## Cleaning Specimens containing this mineral should be handled with utmost care. Due to the microscopic size of the grains, mechanical cleaning is not recommended and can lead to damage or loss of material. If dust removal is necessary, compressed air can be used from a safe distance. ## What to Avoid Avoid contact with all chemicals, acids, and bases. The specimen should not be subjected to ultrasound. The mineral is brittle, so it should be protected from impacts and scratches. ## Storage Specimens should be stored in stable conditions, away from dust and moisture, preferably in a sealed "micromount" box. Avoid sudden temperature changes.

Sources

IMA Mineral List (CNMNC)