Akimotoite is a rare silicate mineral in the ilmenite group of minerals, with the chemical formula .[
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Crystal structure
The crystal structure is similar to that of ilmenite (FeTiO3) with Si and Mg in regular octahedral coordination with oxygen. The Si and Mg octahedra align in discrete layers alternating up the c-axis. The space group is R (trigonal) with a = 4.7284 Å; c = 13.5591 Å; V = 262.94 Å3; Z = 6.[Horiuchi, H., Hirano, M., Ito, E., and Matsui, Y. (1982) MgSiO3 (ilmenite-type): single crystal X-ray diffraction study. American Mineralogist, 67, 788-793]
Occurrence
Akimotoite was found in the Tenham meteorites in Queensland, Australia. It is believed to have
formed as the result of an extraterrestrial shock event. It is the silicon analogue of geikielite (MgTiO3). It was named after physicist (also known as 秋本 俊一) (1925–2004), University of Tokyo.[
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It has also been reported from the Sixiangkou meteorite in the Gaogang District, Jiangsu Province, Taizhou Prefecture, China; the Zagami Martian meteorite, Katsina State, Nigeria and from the Umbarger meteorite, Randall County, Texas.[
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Akimotoite is believed to be a significant mineral in the Earth's mantle at depths of in cooler regions of the mantle such as where a Subduction enters into the lower mantle. Akimotoite is elastically anisotropic and has been suggested as a cause of seismic anisotropy in the lower transition zone and uppermost lower mantle.[Shiraishi, R., Ohtani, E., Kanagawa, K., Shimojuku, A., and Zhao, D. (2008) Crystallographic preferred orientation of akimotoite and seismic anisotropy of Tonga slab. Nature, 455, 657-660]
See also
