Ohtaniite

Chemical formula: Mg₃(Si₀.₅&#₉₇₄₄;₀.₅)Si₂O₈

Ohtaniite is an extremely rare mineral of the wadsleyite group, found exclusively as microscopic inclusions in superdeep diamonds.

## Characteristics Ohtaniite is a magnesium silicate belonging to the wadsleyite group. It is a mineral of immense scientific importance, as its existence confirms processes occurring in the Earth's mantle. It occurs exclusively as microscopic, colorless, anhedral (irregularly shaped) grains trapped within natural diamonds originating from very great depths. The size of individual grains does not exceed 150 micrometers, making them invisible to the naked eye. ## Physical Properties Due to its occurrence only as tiny inclusions, most of its physical properties have not been determined. It is a colorless mineral. Its density, calculated based on its chemical composition and crystal structure, is 3.35 g/cm³. ## Colors and Varieties Only colorless specimens of ohtaniite are known. No colored or commercial varieties are distinguished. ## History and Name The mineral is named in honor of Professor Eiji Ohtani (born 1947) of Tohoku University in Japan, in recognition of his contributions to the field of mineral physics and research into conditions in the Earth's deep interior. Ohtaniite was officially approved by the International Mineralogical Association (IMA) in 2017. The type locality (locus typicus) is the diamond deposits in the Juína region, Mato Grosso state, Brazil. ## Applications Ohtaniite has no commercial or industrial applications. Its significance is purely scientific, providing invaluable information about the composition and conditions in the Earth's mantle transition zone.

Properties

Density: 3.35
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of ohtaniite is impossible without advanced analytical equipment. Recognition is based on chemical analysis (electron microprobe) and structural analysis (Raman spectroscopy, electron diffraction) performed on the inclusion within the diamond. Visually, it is indistinguishable from other colorless inclusions. ## Distinguishing from Similar Minerals The most similar mineral is wadsleyite, to which ohtaniite is closely related. Differentiation requires precise analysis of chemical composition and crystal structure, as ohtaniite is a hydrated variant of wadsleyite with a specific structure. ## Crystal Forms Ohtaniite forms only very small, irregular, anhedral grains. No well-formed crystals have been observed.

Geological environment

## Genesis Ohtaniite is an ultra-high-pressure mineral. It forms under conditions prevailing in the Earth's mantle transition zone, at depths of 410 to 660 kilometers. It is trapped as an inclusion during diamond growth and then rapidly transported to the surface by kimberlitic magmas. ## Mineral Associations This mineral coexists with other high-pressure minerals that also form inclusions in the same "superdeep" diamonds. These include wadsleyite, majorite, and native iron, among others. ## Localities The only confirmed locality for ohtaniite in the world is the alluvial diamond deposits in the Juína region, Mato Grosso state, Brazil.

Rarity

Extremely rare

For collectors

## Quality Criteria Ohtaniite specimens are not subject to standard collector's evaluation criteria, as they are not traded. Their value is purely scientific. A "specimen" is considered a diamond containing an identified and documented ohtaniite inclusion. The most valuable are those that also contain other rare mantle minerals, forming unique mineral assemblages. ## Popular Localities The only known locality from which specimens originate is the Juína region in Brazil. Diamonds from there are known worldwide for containing unique superdeep mineral inclusions.

Care and storage

## Cleaning This mineral occurs exclusively as an inclusion in diamond, and it is not possible to extract or directly clean it. Any care activities apply only to the host diamond. ## What to Avoid Any attempt to mechanically or chemically access the ohtaniite inclusion will cause its irreversible destruction. The host diamond should be protected from damage, extreme temperature changes, and aggressive chemicals. ## Storage Diamond specimens with ohtaniite inclusions are unique scientific objects. They are stored in specialized research collections, protected from all factors that could damage the diamond.

Sources

IMA Mineral List (CNMNC)