Akimotoite
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Akimotoite is a rare
silicate mineral Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...
in the
ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printi ...
group of minerals, with the chemical formula . It is polymorphous with
pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...
and with
bridgmanite Silicate perovskite is either (the magnesium end-member is called bridgmanite) or (calcium silicate known as davemaoite) when arranged in a perovskite structure. Silicate perovskites are not stable at Earth's surface, and mainly exist in the l ...
, a natural
silicate perovskite Silicate perovskite is either (the magnesium end-member is called bridgmanite) or (calcium silicate known as davemaoite) when arranged in a perovskite structure. Silicate perovskites are not stable at Earth's surface, and mainly exist in the l ...
that is the most abundant mineral in Earth's silicate mantle. Akimotoite has a vitreous luster, is colorless, and has a white or colorless streak. It crystallizes in the
trigonal In crystallography, the hexagonal crystal family is one of the six crystal family, crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the tr ...
crystal system in space group R. It is the silicon analogue of
geikielite Geikielite is a magnesium titanium oxide mineral with formula: MgTiO3. It is a member of the ilmenite group. It crystallizes in the trigonal system forming typically opaque, black to reddish black crystals. It was first described in 1892 for an o ...
(MgTiO3).


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 Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...
, Australia. It is believed to have formed as the result of an extraterrestrial shock event. It is the
silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
analogue of
geikielite Geikielite is a magnesium titanium oxide mineral with formula: MgTiO3. It is a member of the ilmenite group. It crystallizes in the trigonal system forming typically opaque, black to reddish black crystals. It was first described in 1892 for an o ...
(MgTiO3). It was named after physicist Syun-iti Akimoto (also known as ) (1925–2004), University of Tokyo. It has also been reported from the Sixiangkou meteorite in the
Gaogang District Gaogang District () is one of three districts of Taizhou, Jiangsu Jiangsu is a coastal Provinces of the People's Republic of China, province in East China. It is one of the leading provinces in finance, education, technology, and tourism, wi ...
,
Jiangsu Province Jiangsu is a coastal province in East China. It is one of the leading provinces in finance, education, technology, and tourism, with its capital in Nanjing. Jiangsu is the third smallest, but the fifth most populous, with a population of 84. ...
, Taizhou Prefecture,
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
; the Zagami Martian meteorite,
Katsina State Katsina State ( ; 𞤤𞤫𞤴𞤣𞤭 𞤳𞤢𞥁𞤭𞤲𞤢) is a state in the northwestern geopolitical zone of Nigeria. It is bordered to the west by Zamfara State, to the east by Kano and Jigawa states, and to the south by Kaduna St ...
,
Nigeria Nigeria, officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf of Guinea in the Atlantic Ocean to the south. It covers an area of . With Demographics of Nigeria, ...
and from the
Umbarger meteorite Umbarger ( ) is a census-designated place in Randall County, Texas, United States. According to the Handbook of Texas, the community had an estimated population of 327 in 2000. The community is part of the Amarillo, Texas Metropolitan Statist ...
,
Randall County, Texas Randall County is a county located in the U.S. state of Texas. As of the 2020 census, its population was 140,753. Its county seat is Canyon. The county was created in 1876 and later organized in 1889. It is named for Horace Randal, a Confed ...
. Akimotoite is believed to be a significant mineral in the
Earth's mantle Earth's mantle is a layer of silicate mineral, silicate rock between the Earth's crust, crust and the Earth's outer core, outer core. It has a mass of and makes up 67% of the mass of Earth. It has a thickness of making up about 46% of Earth's ...
at depths of in cooler regions of the mantle such as where a subducted slab 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

*
Glossary of meteoritics This is a glossary of terms used in meteoritics, the science of meteorites. # * 2 Pallas – an asteroid from the asteroid belt and one of the likely parent bodies of the CR meteorites. * 4 Vesta – second-largest asteroid in the asteroid bel ...


References

Oxide minerals Meteorite minerals Trigonal minerals Minerals in space group 148 {{silicate-mineral-stub