Tanohataite

Chemical formula: LiMn<sup>2+</sup><sub>2</sub>Si<sub>3</sub>O<sub>8</sub>(OH)

Tanohataite is a rare lithium manganese silicate, forming brown, tabular crystals, discovered in Japan.

## Characteristics Tanohataite is a very rare mineral from the silicate group, belonging to the pyroxenoids. Chemically, it is a hydrated lithium manganese silicate. It occurs as small, tabular or bladed crystals, reaching up to 1 mm in size. It typically forms radial or randomly oriented aggregates and clusters. Its structure is closely related to minerals such as serandite, pectolite, and bustamite. ## Physical Properties Tanohataite crystals exhibit a vitreous luster. The mineral is transparent to translucent. It has a hardness of approximately 5.5 on the Mohs scale and a density of 3.46 g/cm³. It shows perfect cleavage in two directions, which is characteristic of its crystal structure. ## Colors and Varieties Tanohataite has a characteristic brown to orange-brown color. No color varieties or commercial varieties are known. ## History and Name The mineral was discovered in the Tanohata manganese deposit in Iwate Prefecture on Honshu Island, Japan. It was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 1999. Its name comes directly from its discovery location (type locality). ## Applications Due to its extreme rarity, tanohataite has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals.

Properties

Mohs hardness
5.5
Luster
Vitreous
Streak
Light brown
Density
3.46
Cleavage
Perfect on {100} and {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Identifying tanohataite under amateur conditions is practically impossible. It requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). Preliminary identification can be based on its brown color, tabular crystal habit, and co-occurrence with other rare manganese minerals at the type locality. ## Distinguishing from Similar Minerals It can be confused with other manganese silicates of similar color, such as some varieties of rhodonite, bustamite, or nambulite. Definitive differentiation is possible only through chemical composition analysis (presence of lithium) and crystallographic data. ## Crystal Forms Tanohataite crystallizes in the triclinic system. It forms flattened, tabular or bladed crystals, often grouped into radial or disordered aggregates.

Geological environment

## Genesis Tanohataite forms as a result of hydrothermal or metamorphic processes within manganese deposits. At the type locality (Tanohata mine), it occurs in veins cutting manganese-rich rocks, such as rhodochrosite tephrite. ## Mineral Associations This mineral co-occurs with other, often rare, manganese minerals. At the Tanohata mine, it has been found in association with minerals such as nambulite, rhodochrosite, tephroite, galaxite, alabandite, roscoelite, and quartz. ## Localities The only confirmed and described occurrence of tanohataite in the world is the Tanohata mine, in Iwate Prefecture, Tōhoku region on Honshu Island, Japan. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a tanohataite specimen depends primarily on the presence of well-formed, even microscopic, crystals with a distinct brown color. Due to its extreme rarity, any analytically confirmed specimen is valuable. The most desirable are rich clusters of crystals on a contrasting rock matrix, visible under a microscope. ## Popular Localities The only source of specimens is the Tanohata mine in Japan. Material from this locality is extremely difficult to acquire and appears on the collector's market sporadically.

Care and storage

## Cleaning Due to its rarity and delicacy, cleaning should be kept to an absolute minimum. If necessary, compressed air can be used to remove dust. Avoid contact with water and any chemical agents. ## What to Avoid Avoid ultrasonics, steam cleaners, acids, solvents, and sudden temperature changes. The mineral is sensitive to chemicals that can damage its surface. ## Storage Tanohataite specimens are usually very small (micromounts) and should be stored in specialized perky boxes, protecting them from dust, humidity, and mechanical damage. Avoid exposure to direct sunlight.

Sources

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