Kinoshitalite

Chemical formula: BaMg₃(Si₂Al₂)O₁₀(OH)₂

Kinoshitalite is a rare mineral from the mica group, brittle, platy, with a brownish color and vitreous to pearly luster.

## Characteristics Kinoshitalite is a rare mineral belonging to the mica group, specifically to the so-called brittle micas. It forms small, thin, platy or scaly crystals, often aggregated into rosette-like or platy clusters. Individual lamellae are flexible but brittle, which distinguishes it from common micas. It usually occurs disseminated in the host rock. ## Physical Properties Kinoshitalite crystals exhibit a hardness in the range of 4.5 on the Mohs scale, making them harder than most common micas, such as biotite or muscovite. Its density is approximately 3.31 g/cm³. The mineral's lamellae are flexible, yet brittle. The luster is vitreous to pearly, especially noticeable on cleavage planes. ## Colors and Varieties This mineral most commonly occurs in colors ranging from yellowish-brown and reddish-brown to almost black. No named color varieties or commercial varieties are distinguished. ## History and Name Kinoshitalite was first described in 1973 by M. Yoshii, K. Maeda, and T. Kato. Its name honors the Japanese geologist and mineralogist, Professor Kameki Kinoshita (1896-1974) of Kyushu Institute of Technology, in recognition of his contributions to the study of Japanese ore deposits. ## Uses Due to its rarity and small crystal size, kinoshitalite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and for scientists.

Properties

Mohs hardness
2.5-3
Color
Yellow brown to colorless
Luster
Vitreous to pearly
Streak
Light brown
Density
3.30
Cleavage
{001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Kinoshitalite can be identified by its platy or scaly form, brownish color, and relatively high (for a mica) hardness. Its brittleness is characteristic – the lamellae, unlike biotite, break easily. It occurs in a specific geological environment – metamorphic rocks and skarns rich in manganese and barium. ## Distinguishing from Similar Minerals It is most easily confused with other dark-colored micas, primarily biotite. Kinoshitalite is harder than biotite (4.5 compared to 2.5-3 for biotite) and more brittle. Final distinction from other rare brittle micas, such as anandite or clintonite, requires advanced chemical (EDS) or X-ray (XRD) analyses. ## Crystal Forms Crystals are tabular or platy, often with a pseudohexagonal outline. They usually form scaly, rosette-like aggregates or stacks of lamellae. Single, well-formed crystals are rarely found.

Geological environment

## Genesis Kinoshitalite is a mineral of metamorphic origin. It forms under conditions of contact metamorphism, in skarns or other metamorphic rocks that have undergone metasomatism. Its formation is associated with the presence of barium, magnesium, and aluminum in the environment, often in manganese ore deposits. ## Mineral Associations This mineral coexists with other minerals typical of metamorphic rocks and skarns, such as tephroite, rhodochrosite, celsian, alleghanyite, willemite, phlogopite, calcite, and quartz. ## Localities The most important and classic localities for this mineral are in Japan, from where it was first described (Noda-Tamagawa mine, Iwate Prefecture, and Hokkejino mine, Kyoto Prefecture). It is also known from the Kombat mine in Namibia, from the Franklin deposit in New Jersey (USA), and from several locations in Sweden (e.g., Långban).

Rarity

Rare

For collectors

## Quality Criteria The most prized by collectors are specimens with well-formed, sharp crystals with a pseudohexagonal outline, forming aesthetic, rosette-like aggregates. An intense, reddish-brown color and distinct luster are also important. Contrasting placement on a light rock matrix, for example, on white calcite, significantly enhances the visual appeal and value of the specimen. Due to the mineral's rarity, even small but well-defined crystals are sought after. ## Popular Localities The best specimens in the world are considered to be those from the Kombat mine in Namibia, which yielded relatively large and well-formed crystals. Classic, though usually smaller, are specimens from the type locality in Japan (Noda-Tamagawa). The American Franklin deposit also provided microscopic but well-identified crystals.

Care and storage

## Cleaning Kinoshitalite specimens should be cleaned very carefully, using a soft brush to remove dust. The use of compressed air from a safe distance is permissible. Due to its platy structure and brittleness, washing in water should be avoided, as water could penetrate between the lamellae and weaken the aggregate structure. ## What to Avoid Contact with acids and other chemicals must be strictly avoided. The mineral is brittle, so it must be protected from impacts, scratching, and bending of the lamellae. It should not be heated or subjected to ultrasound. ## Storage Kinoshitalite specimens are best stored in enclosed display boxes that protect against dust and mechanical damage. Avoid placing other minerals on top of them. Due to the small size of the crystals, it is often stored mounted on a stand or in a membrane box.

External references

Sources

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