Tokyoite

Chemical formula: Ba<sub>2</sub>Mn<sup>3+</sup>(V<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)

Tokioite is a very rare mineral from the brackebuschite group, distinguished by its reddish-brown color and occurrence in manganese deposits.

## Characteristics Tokioite is a mineral belonging to the apatite supergroup and the brackebuschite group. It is a barium manganese vanadate. It occurs in the form of very small, tabular or bladed crystals, usually not exceeding 0.3 mm, forming rosette-like or radial aggregates. Its most characteristic feature is its intense, reddish-brown color. ## Physical Properties Tokioite crystals exhibit a strong luster, described as adamantine or subadamantine. The mineral is transparent to translucent. Due to the small size of the crystals, hardness has not been precisely measured, but it is estimated to be 4-5 on the Mohs scale. The density calculated based on the chemical formula and unit cell parameters is approximately 4.75 g/cm³. ## Colors and Varieties This mineral is monochromatic – it occurs in shades from reddish-brown to orange-brown. No color varieties or commercial varieties are known. ## History and Name Tokioite was discovered in the Shiromaru mine in Tokyo Prefecture, Japan. It was described and approved as a new mineral by the International Mineralogical Association (IMA) in 2003. Its name comes from its type locality – Tokyo Prefecture, which is rare, as few minerals are named after such a large metropolis. ## Uses Due to its extreme rarity and microscopic crystal size, tokioite has no industrial applications. It is solely an object of scientific and collecting interest for specialized micromineral collectors.

Properties

Mohs hardness
4-5
Luster
Adamantine, Resinous
Streak
Light brown
Density
4.75
Cleavage
Good on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Tokioite is primarily recognizable by its unique appearance: reddish-brown, tabular crystals forming rosette-like aggregates. The luster, described as adamantine, is also a characteristic feature. However, definitive identification requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS), due to its co-occurrence with other visually similar minerals. ## Distinguishing from Similar Minerals Tokioite can be confused with other minerals from the brackebuschite group, such as gamagarite, with which it often co-occurs. However, gamagarite usually has a darker, almost black color and a different crystal morphology. Distinguishing it from other rare manganese vanadates without specialized equipment is practically impossible. ## Crystal Forms Tokioite crystals are very small, typically measuring up to 0.3 x 0.1 x 0.01 mm. They have a tabular or bladed habit, often flattened. They form characteristic, radial or rosette-like aggregates on the surface of the host rock.

Geological environment

## Genesis Tokioite forms under low-temperature hydrothermal conditions, within veins cutting weathered, Paleozoic rocks (mainly cherts) associated with manganese deposits. It is a product of the alteration of earlier manganese and vanadium minerals. ## Mineral Associations This mineral co-occurs with other rare manganese and vanadium minerals. In its type locality (Shiromaru mine), it was found in association with gamagarite, quartz, braunite, piemontite, wallkilldellit-(Mn), and potassicleakeite. ## Localities The only confirmed and detailed described occurrence of tokioite in the world is its type locality – Shiromaru mine, Okutama, Tokyo Prefecture, in the Kantō region of Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a tokioite specimen is primarily assessed based on the abundance and development of its crystals. The most prized specimens are those with numerous, well-formed, rosette-like aggregates of an intense, reddish-brown color. The contrast with the light host rock (quartz), which highlights the colorful crystals, is also important. Due to the microscopic nature of the mineral, the size of individual crystals, even if measured in fractions of a millimeter, is significant. ## Popular Localities All specimens available on the collector's market come from a single location in the world – the Shiromaru mine in Japan. This is the only known locality for this mineral, making each specimen unique from a locality perspective.

Care and storage

## Cleaning Tokioite specimens, due to their microscopic size and delicacy, should be cleaned very carefully. The safest method is to use compressed air (from a safe distance) to remove dust. Mechanical cleaning and contact with water, which could damage the host rock, should be avoided. ## What to Avoid Contact with chemicals, especially acids, which can destroy the mineral, must be absolutely avoided. Specimens should be protected from high temperatures, shocks, and ultrasound. Prolonged exposure to strong sunlight is not recommended. ## Storage The best way to store tokioite is to place it in a specialized micromount box, which protects delicate crystals from mechanical damage and dust. The specimen should be stored under stable humidity and temperature conditions.

External references

Sources

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