Akasakaite-(La)

Chemical formula: CaLa(Al<sub>2</sub>Mn<sup>2+</sup>)(Si<sub>2</sub>O<sub>7</sub>)(SiO<sub>4</sub>)O(OH)

Akasakaite-(La) is an extremely rare mineral from the epidote supergroup, found as microscopic, brownish-black grains in Japan.

## Characteristics Akasakaite-(La) is a mineral belonging to the epidote supergroup. It occurs as very small, anhedral grains, not exceeding 0.3 mm in size. These grains are embedded in the host rock. The mineral is brownish-black and has a vitreous luster. ## Physical Properties The mineral's hardness on the Mohs scale is 6. It is translucent, with a calculated density of approximately 4.03 g/cm³. It exhibits good cleavage in one direction. ## Colors and Varieties It is known exclusively in brownish-black. No color varieties or commercial forms have been identified. ## History and Name The mineral was described in 2014 by Satomi and collaborators. Its name honors Masahide Akasaka (born 1953), a Japanese professor from Shimane University, for his contributions to the study of epidote group mineralogy. The suffix "-(La)" indicates the dominance of lanthanum in its chemical composition, distinguishing it from its cerium-dominant analog, akasakaite-(Ce). ## Uses Due to its extreme rarity and microscopic size, akasakaite-(La) has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals and micromounts.

Properties

Mohs hardness
6
Luster
Vitreous
Streak
Light brown
Density
4.03
Cleavage
Good on {001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of akasakaite-(La) based on visual characteristics is impossible. Recognition requires advanced analytical techniques, such as X-ray microanalysis (EDS/WDS), to confirm its unique chemical composition, especially the dominance of lanthanum. The discovery location (type locality) and co-occurring minerals are also crucial. ## Distinguishing from Similar Minerals This mineral can be confused with other dark epidote group minerals, such as allanite-(Ce) or ferriallanite-(La). Definitive distinction is only possible through precise chemical analysis, which will show that lanthanum is the dominant rare earth element and manganese occurs in the divalent oxidation state (Mn²⁺). ## Crystal Forms Akasakaite-(La) does not form well-developed crystals. It occurs exclusively as irregular, anhedral grains embedded in the rock.

Geological environment

## Genesis This mineral forms under hydrothermal conditions. Its occurrences have been found in veins cutting calc-silicate xenoliths (skarns) trapped within an intruding biotite-hornblende adamellite. ## Mineral Associations Akasakaite-(La) co-occurs with minerals such as hedenbergite, allanite-(Ce), clinozoisite, quartz, calcite, andradite, vesuvianite, and wollastonite. ## Localities The only confirmed locality for this mineral worldwide is its type locality – the Kiura (Ohgidani) mine in Saiki City, Oita Prefecture, Kyushu Island, Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria For collectors, the most important criterion is the confirmation of the specimen's authenticity from the only known locality. Value increases with the abundance of akasakaite-(La) grains on the rock matrix and the presence of well-formed associated minerals. Aesthetics are secondary for such a rare species, available mainly as micromounts. ## Popular Localities The most valuable and only specimens come from the Kiura mine in Japan.

Care and storage

## Cleaning Specimens should be cleaned very carefully, preferably with a soft brush or a stream of compressed air to remove dust. Due to the microscopic nature of the grains, washing in water is not recommended and may lead to material loss. ## What to Avoid Avoid contact with all chemicals, especially acids. Ultrasonic cleaning is absolutely forbidden, as it can damage delicate grains embedded in the rock matrix. High temperatures should also be avoided. ## Storage Specimens of akasakaite-(La) should be stored in specialized "micromount" boxes, which protect them from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight.

Sources

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