Manganiakasakaite-(La)

Chemical formula: CaLa<sup>3+</sup>Mn<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, a black calcium, lanthanum, and manganese silicate, known only from one locality in Japan.

## Characteristics Manganiakasakaite-(La) is a very rare mineral belonging to the epidote supergroup. It forms small, imperfectly developed, prismatic crystals or grains not exceeding 0.3 mm in size. It is opaque, black in color, and has a submetallic luster. Due to its microscopic size and occurrence in only one location worldwide, it is primarily of scientific interest and for specialized collectors of rare minerals. ## Physical Properties This mineral is characterized by a submetallic luster and is completely opaque. Its density, calculated from its chemical composition and unit cell parameters, is 4.13 g/cm³. Its hardness has not yet been determined. ## Colors and Varieties The only known color of this mineral is black. No color or commercial varieties have been distinguished. ## History and Name The mineral's name reflects its chemical composition and structural relationships. The "Mangani-" prefix indicates the dominant role of manganese, while the "-(La)" suffix (according to Levinson's nomenclature) signifies that lanthanum is the dominant rare earth element in a specific structural position. The name "akasakaite" refers to the mineral akasakaite, which was named after the town of Akasaka in Japan. Manganiakasakaite-(La) was officially recognized by the International Mineralogical Association (IMA) in 2013. It was described by Japanese mineralogists Chiyoko Henmi, Isao Kusachi, and Satomi Inaba. ## Applications As a mineral of microscopic size and extreme rarity, manganiakasakaite-(La) has no industrial applications. Its significance is purely scientific and for collectors.

Properties

Luster
Sub-metallic
Streak
Greyish brown
Density
4.13
Cleavage
Good on {001}
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Visual identification is practically impossible and requires specialized equipment. Clues may include: black color, submetallic luster, occurrence as small prismatic crystals, and most importantly, mineral paragenesis. Definitive identification relies on chemical analysis (e.g., by EDS or WDS) to confirm the unique composition with dominant lanthanum and manganese. ## Distinguishing from Similar Minerals Manganiakasakaite-(La) can be confused with other black minerals from the epidote group, such as allanite, ferriallanite, or manganiandrosite, as well as other black, opaque oxide and silicate minerals (e.g., ilmenite, braunite) occurring in similar environments. Key to differentiation is the determination of lanthanum dominance over other rare earth elements and specific manganese proportions, which is only possible using advanced analytical techniques. ## Crystal Forms This mineral forms poorly developed (subhedral) to xenomorphic (anhedral) grains up to 0.3 mm in size. Short, prismatic crystals have also been observed.

Geological environment

## Genesis Manganiakasakaite-(La) forms under conditions of contact metamorphism. Its only known locality is a manganese ore deposit (mainly braunite) developed within Paleozoic limestones that were intruded by a quartz syenite dike. ## Mineral Associations This mineral coexists with a rich assemblage of minerals. The most common include: braunite, jacobsite, rhodochrosite, quartz, celsian, anorthoclase, aegirine, richterite, and vesuvianite. ## Localities The only confirmed occurrence of manganiakasakaite-(La) in the world is the Kiura (Shin-Kiura) mine in Saiki City, Oita Prefecture, Kyushu Island, Japan. This is the type locality for this mineral.

Rarity

Extremely rare

For collectors

## Quality Criteria For such a rare micromineral, the collector's value of a specimen is determined by several factors. Samples with clearly developed, even if only partially, prismatic crystals are most highly prized. A rich association with other rare minerals on the same rock matrix is also important. The size and abundance of manganiakasakaite-(La) grains on the specimen also increase its attractiveness. ## Popular Localities The only specimens available on the collector's market come from the type locality – the Kiura mine in Japan. Obtaining material from this location is extremely difficult, making each specimen unique.

Care and storage

## Cleaning Specimens of this mineral are typically microscopic crystals on a rock matrix. Mechanical cleaning is highly risky. If necessary, compressed air can be used to remove dust or a very soft, dry brush. Avoid contact with water and any chemical agents. ## What to Avoid The mineral should be protected from acids, solvents, and ultrasonic cleaners. Rapid temperature changes should also be avoided, as they could cause cracks in the host rock and damage delicate crystals. ## Storage It is recommended to store specimens in stable conditions, away from moisture and contaminants. The safest method is to place the mineral in a "micromount" box, which protects it from mechanical damage and dust while allowing observation under a microscope.

Sources

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