Watatsumiite

Chemical formula: KNa₂LiMn²⁺₂V⁴⁺₂Si₈O₂₄

Watatsumiite is a very rare, green silicate from the neptunite group, discovered in Japan and valued for its unique chemical composition.

## Characteristics Watatsumiite is a very rare mineral belonging to the neptunite group. It forms small, transparent crystals with a characteristic, vibrant color, resembling peridot. It typically occurs as single, well-formed crystals or small aggregates, grown on other minerals. Its unique chemical composition, containing potassium, sodium, lithium, manganese, and vanadium, makes it an object of scientific interest. ## Physical Properties This mineral is characterized by a hardness of 5.5-6 on the Mohs scale, placing it in the same category as feldspars. It has a vitreous luster and a conchoidal fracture. It is transparent, allowing for observation of its internal structure and clarity. ## Colors and Varieties Watatsumiite occurs in shades of green, most often described as peridot-green or yellowish-green. No distinct color varieties or commercial names have been identified. ## History and Name The mineral was discovered and described in 2000. Its name comes from Watatsumi-no-kami, a Japanese sea deity, which refers to the location where the first specimens were found in Japan. The type locality is the Tanohata mine in Iwate Prefecture. ## Uses Due to its extreme rarity, watatsumiite has no industrial applications. Its significance is purely scientific and collectible.

Properties

Mohs hardness
5.5-6
Luster
Vitreous
Streak
White with a greenish tint
Density
0
Cleavage
on {110} poor
Fracture
Conchoidal
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features include its characteristic peridot-green color, vitreous luster, occurrence as small, prismatic crystals, and mineral associations. Final confirmation requires advanced chemical analysis due to its resemblance to other minerals. ## Distinguishing from Similar Minerals It can be confused with other green silicates, such as peridot (olivine) or epidote. It is distinguished from them by hardness, crystal habit, and unique occurrence environment. From other minerals in the neptunite group (e.g., manganoneptunite), it differs mainly in chemical composition, which cannot be determined without specialized equipment. ## Crystal Forms Watatsumiite crystals are usually small and have a prismatic habit. They crystallize in the monoclinic system.

Geological environment

## Genesis Watatsumiite forms in manganese ore deposits that have undergone metamorphic processes. It is a product of specific geochemical conditions, requiring the presence of vanadium, lithium, and other elements that comprise its composition. ## Mineral Associations This mineral co-occurs with other manganese minerals and silicates. At its type locality, it was found in association with sugilite, serandite, rhodonite, and quartz. ## Localities The only confirmed and described occurrence of watatsumiite in the world is its type locality – the Tanohata mine, in Iwate Prefecture, Japan.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens are those with sharp, well-formed, and undamaged crystals of intense, pure green color. An aesthetic composition with associated minerals (matrix), such as contrasting white quartz, is also important. Due to the small size of the crystals, even small specimens are considered valuable. ## Popular Localities The only source of collectible specimens is the Tanohata mine in Japan. Material from this locality is extremely rare and sought after by specialized collectors.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. If necessary, compressed air can be used. Avoid contact with water and any chemical agents. ## What to Avoid Avoid ultrasonic cleaners, chemical agents (acids, bases, solvents), and sudden temperature changes. The mineral is brittle and sensitive to impact. ## Storage It is recommended to store specimens in stable conditions, in a closed display box, away from direct sunlight and dust. It is best to keep it in its original box from the place of purchase to protect delicate crystals from damage.

External references

Sources

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