Yoshimuraite

Chemical formula: Ba<sub>4</sub>Mn<sup>2+</sup><sub>4</sub>Ti<sup>4+</sup><sub>2</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>O<sub>2</sub>(OH)<sub>2</sub>

Yoshimuraite is a very rare mineral from the sorosilicate group, forming characteristic, tabular crystals of a brownish-black color and vitreous luster.

## Characteristics Yoshimuraite is a complex silicate, phosphate, and oxide of barium, manganese, and titanium. It occurs as aggregates or individual, well-formed crystals with a tabular or lamellar habit, often elongated and flattened. Its color is usually dark brown to black, and on thin edges, it can be translucent brownish. It is a brittle mineral. ## Physical Properties The mineral is characterized by a hardness of 4.5 on the Mohs scale and a density of approximately 4.4 g/cm³. The luster is vitreous, and on cleavage surfaces, it can be pearly. It is translucent in thin fragments, becoming opaque in thicker pieces. ## Colors and Varieties Dark brown to black is the dominant color. No named varieties of this mineral have been distinguished. ## History and Name The mineral was discovered in the Noda-Tamagawa mine in Iwate Prefecture, Japan. It was described in 1961 by Japanese mineralogists Takeo Watanabe, Yoshio Takeuchi, and Jun Ito. The name honors Professor Toyofumi Yoshimura (1905–1991), a Japanese mineralogist and petrologist from Kyushu University, for his contributions to the study of manganese deposits in Japan. ## Uses Due to its extreme rarity, yoshimuraite has no industrial application. It is solely an object of scientific and collector interest.

Properties

Mohs hardness
4.5
Luster
Vitreous, Pearly
Streak
Light brown
Density
4.4
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Triclinic

Diagnostic features

## Identification Characteristic features of yoshimuraite include its black or dark brown color, tabular or lamellar crystal habit, perfect cleavage in one direction, and pearly luster on cleavage planes. Its occurrence in a specific geological environment (manganese deposits) is also an important clue. ## Distinguishing from Similar Minerals It can be confused with other black, tabular minerals, such as some micas (e.g., biotite) or pyroxenoids. It differs from biotite by its greater hardness and density, and the lack of elasticity in its lamellae. Unlike many similar manganese minerals, yoshimuraite has a lighter, brownish streak. ## Crystal Forms Crystals are tabular, flattened parallel to the {010} cleavage plane, and elongated along the crystallographic a-axis. They often form radial or fan-shaped aggregates.

Geological environment

## Genesis Yoshimuraite is a mineral of metamorphic origin. It forms in manganese deposits that have undergone contact metamorphism under the influence of igneous rock intrusions. It occurs in veins cutting through rhodochrosite deposits and other manganese-rich rocks. ## Mineral Associations It co-occurs with minerals such as tephroite, galaxite, rhodochrosite, pyroxmangite, alabandite, as well as rarer manganese minerals like sonolite or alleghanyite. ## Localities The most important and classic locality, from which the best specimens originate, is the Noda-Tamagawa mine in Iwate Prefecture, Japan. This mineral has also been identified in several other locations worldwide, including manganese ore mines in the Baikal region of Russia and the Kombat mine in Namibia; however, specimens from these localities are much rarer and less known.

Rarity

Very rare

For collectors

## Quality Criteria The most prized yoshimuraite specimens are those with well-formed, sharp crystals with distinct luster, forming aesthetic, radial aggregates. Contrast with a light rock matrix, such as rhodochrosite, significantly enhances the visual and collectible value of the specimen. Crystal size is a key factor – specimens with crystals exceeding a centimeter are considered exceptional. ## Popular Localities By far the most desired and well-known place of origin is the Noda-Tamagawa mine in Japan. Specimens from this locality are considered the global standard for this mineral.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to its perfect cleavage, extreme caution must be exercised. The use of water is not recommended, and if necessary, it should be distilled water, after which the specimen must be thoroughly dried immediately. ## What to Avoid Avoid contact with all chemicals, including acids and strong bases. The mineral is brittle and sensitive to impacts and sudden temperature changes. It should not be cleaned in ultrasonic cleaners. ## Storage It is recommended to store specimens in stable conditions, in a closed display box, to protect them from dust, mechanical damage, and moisture. Its brittleness and perfect cleavage make it prone to crumbling, so it should be isolated from other minerals.

Sources

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