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, silica (silicon dioxide, ) is usually consid ...

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, printing ...

group of minerals, with the chemical formula . It is polymorphous with

pyroxene The pyroxenes (commonly abbreviated to ''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 calcium (Ca), sodium (Na), iron (Fe I ...

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 lo ...

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 families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal ...

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 ...

(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 ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , establishe ...

, Australia. It is believed to have formed as the result of an extraterrestrial shock event. It is the

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

analogue of

(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,

Jiangsu Province Jiangsu (; ; pinyin: Jiāngsū, alternatively romanized as Kiangsu or Chiangsu) is an eastern coastal province of the People's Republic of China. It is one of the leading provinces in finance, education, technology, and tourism, with its c ...

, Taizhou Prefecture,

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...

; the Zagami Martian meteorite,

Katsina State Katsina State ''(Hausa: Jihar Katsina) (Fula: Leydi Katsina 𞤤𞤫𞤴𞤣𞤭 𞤳𞤢𞥁𞤭𞤲𞤢)'' is a state in the northwestern geopolitical zone of Nigeria. Katsina State was created in 1987, when it split from Kaduna State. Today, K ...

Nigeria Nigeria ( ), , ig, Naìjíríyà, yo, Nàìjíríà, pcm, Naijá , ff, Naajeeriya, kcg, Naijeriya officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf o ...

and from the Umbarger meteorite,

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 Confede ...

. Akimotoite is believed to be a significant mineral in the

Earth's mantle Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of 4.01 × 1024 kg and thus makes up 67% of the mass of Earth. It has a thickness of making up about 84% of Earth's volume. It is predominantly so ...

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

References

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

Crystal structure

Occurrence

See also

References