Akimotoite

Chemical formula: MgSiO<sub>3</sub>

Akimotoite is a magnesium silicate with an ilmenite structure, formed under extremely high-pressure conditions, found mainly in meteorites.

## Characteristics Akimotoite is a high-pressure polymorph of magnesium silicate (MgSiO₃), sharing its chemical formula with the more common enstatite, but possessing a distinct, denser ilmenite-type crystal structure. This mineral does not form crystals visible to the naked eye. It occurs exclusively as microscopic, colorless grains, most often irregularly shaped, within heavily shocked meteorites. Its significance is purely scientific, providing crucial information about processes occurring during celestial impacts and about conditions prevailing deep within the Earth. ## Physical Properties Akimotoite grains are typically transparent. Due to the microscopic size of the crystals, most physical properties, such as hardness or luster, have not been precisely determined for natural samples. The mineral's density, calculated based on its crystal structure, is approximately 3.57 g/cm³, which is significantly higher than that of enstatite (approx. 3.2 g/cm³). ## Colors and Varieties Akimotoite is colorless. No colored varieties or trade names are known. ## History and Name The mineral is named in honor of Syun-iti Akimoto (1925–2002), a Japanese geophysicist and pioneer in the study of minerals under high-pressure conditions. It was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 1999. It was first identified in the Tenham meteorite, which fell in Australia. ## Applications Akimotoite has no commercial or industrial applications. It is of interest solely in scientific research, particularly in mineralogy, planetology, and geophysics, as an indicator of extreme pressures and a key component in models of Earth's mantle structure.

Properties

Density
3.57
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of akimotoite is impossible without advanced laboratory equipment. It cannot be recognized based on visual characteristics or simple tests. Confirmation of its presence requires the use of analytical techniques such as electron microprobe analysis (EMPA) to determine chemical composition and X-ray diffraction (XRD) or Raman spectroscopy to confirm its unique crystal structure. ## Distinguishing from Similar Minerals Under microscopic examination, akimotoite must be distinguished from other coexisting high-pressure minerals, such as ringwoodite, wadsleyite, majorite, or bridgmanite. This distinction relies solely on precise measurements of chemical composition and crystallographic data obtained using specialized apparatus. ## Crystal Forms Akimotoite occurs as anhedral (irregular) or subhedral (partially formed) grains on the order of micrometers in size. It forms aggregates embedded in the meteorite's rock matrix, often in close proximity to veins formed by rock melting during impact.

Geological environment

## Genesis Akimotoite is a product of shock metamorphism. It forms as a result of the phase transformation of pyroxene group minerals (mainly enstatite) under extremely high pressures (above 20 GPa) and temperatures, generated during meteorite impacts. It is also considered an important component of Earth's mantle transition zone, at depths of approximately 520 to 660 km, where it forms under stable high-pressure conditions. ## Mineral Associations In meteorites, akimotoite most often coexists with other high-pressure minerals such as ringwoodite, wadsleyite, majorite, as well as remnants of primary minerals like olivine and pyroxene. It may also be accompanied by glass formed from rock melting. ## Localities The most important and first confirmed locality is the Tenham meteorite (L6 chondrite), which fell in 1879 in Queensland, Australia. Akimotoite has also been identified in other heavily shocked chondrites, e.g., in the L'Aigle meteorite (France), and in some meteorites originating from Mars (shergottites).

Rarity

Extremely rare

For collectors

## Quality Criteria Akimotoite is not a mineral acquired and evaluated in terms typical of specimen collecting. Its value is purely scientific. For research institutions and specialized meteorite collections, a "specimen" is usually a polished thin section or a fragment of a meteorite in which the presence of akimotoite has been analytically confirmed. The value of such material does not depend on aesthetics, but on its scientific significance and the rarity of the meteorite itself. ## Popular Localities Since akimotoite is not a mined mineral but only found in specific extraterrestrial bodies, the names of meteorites are considered "localities." The most well-known are Tenham (Australia) and L'Aigle (France).

Care and storage

## Cleaning Specimens containing akimotoite (meteorite fragments) should not be cleaned under amateur conditions. Any attempt at cleaning, especially with chemicals or ultrasonics, can irreversibly destroy the microscopic mineral grains and damage the structure of the entire specimen. Cleaning and conservation of meteorites should be left exclusively to specialists. ## What to Avoid Avoid all mechanical manipulation, contact with chemicals (acids, bases, solvents), moisture, and sudden temperature changes. Meteorite specimens can be susceptible to corrosion in humid environments. ## Storage Meteorite fragments containing akimotoite should be stored under stable, dry conditions. Specialized boxes with membranes or containers with desiccants are recommended to protect against dust, moisture, and mechanical damage.

External references

Sources

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