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Ringwoodite is a high-pressure phase of Mg2SiO4 formed at high temperatures and pressures of the Earth's mantle between 525 and 660 km depth. It is polymorphous with the olivine phase forsterite (a magnesium iron silicate). Ringwoodite is notable for being able to contain hydroxide ions (oxygen and hydrogen atoms bound together) within its structure.〔Ye, Y., D.A. Brown, J. R. Smyth, W.R. Panero, S.D. Jacobsen, Y.-Y. Chang, J.P. Townsend, S.M. Thomas, E. Hauri, P. Dera, and D.J. Frost (2012). ("Compressibility and thermal expansion study of hydrous Fo100 ringwoodite with 2.5(3) wt% H2O" ). ''American Mineralogist'' 97, 573-582.〕 Combined with evidence of its occurrence deep in the Earth's mantle, this suggests that there is from one to three times the world ocean's equivalent of water in the mantle transition zone from 410 to 660 km deep.〔 This mineral was first identified in the Tenham meteorite in 1969,〔R A. Binns, R. J. Davis, and No S. J. B Reed (1969). "Ringwoodite, natural (Mg,Fe)2SiO4 Spinel group in the Tenham meteorite. ''Nature'' 221,943 944.〕 and it is inferred to be present in large quantity in the Earth’s mantle. Ringwoodite was named after the Australian earth scientist Ted Ringwood (1930–1993), who studied polymorphic phase transitions in the common mantle minerals olivine and pyroxene at pressures equivalent to depths as great as about 600 km. Olivine, wadsleyite, and ringwoodite are polymorphs found in the upper mantle of the earth. At depths greater than about 660 km, other minerals, including some with the perovskite structure, are stable. The properties of these minerals determine many of the properties of the mantle. ==Introduction== Ringwoodite is polymorphous with forsterite, (Mg)2SiO4, and has a spinel structure. Spinel group minerals crystallize in the isometric system with an octahedral habit. Olivine is most abundant in the upper mantle, above about 410 km; the olivine polymorphs wadsleyite and ringwoodite are thought to dominate the transition zone of the mantle, a zone present from about 410 to 660 km depth. Ringwoodite is thought to be the most abundant mineral phase in the lower part of Earth’s transition zone. The physical and chemical property of this mineral partly determine properties of the mantle at those depths. The pressure range for stability of ringwoodite lies in the approximate range from 18 to 23 GPa. Apart from the mantle, natural ringwoodite has been found in many shocked chondritic meteorites, in which the ringwoodite occurs as fine-grained polycrystalline aggregates.〔Chen. M, El Goresy A., and Gillet P. (2004). "Ringwoodite lamellae in olivine: Clues to olivine–ringwoodite phase transition mechanisms in shocked meteorites and subducting slabs". ''PNAS''.〕 Natural ringwoodite generally contains much more Mg than Fe but can form a gapless solid solution series from the pure Mg endmember to the pure Fe endmember. The latter has been discovered in a natural sample only recently and was named ahrensite, in honor of US mineral physicist Thomas J. Ahrens (1936–2010). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ringwoodite」の詳細全文を読む スポンサード リンク
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