| Ringwoodite | |
|---|---|
 Crystal (~150 micrometers across) of Fo90 composition blue ringwoodite synthesized at 20 GPa and 1200 °C. | |
| General | |
| Category | Nesosilicates Spinel group |
| Formula (repeating unit) | Magnesium silicate (Mg2SiO4) |
| IMA symbol | Rgd[1] |
| Strunz classification | 9.AC.15 |
| Crystal system | Cubic |
| Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m) |
| Space group | Fd3m |
| Unit cell | a = 8.113 Å; Z = 8 |
| Identification | |
| Colour | Deep blue, also red, violet, or colourless (pure Mg2SiO4) |
| Crystal habit | Microcrystalline aggregates |
| Diaphaneity | Semitransparent |
| Specific gravity | 3.90 (Mg2SiO4); 4.13 ((Mg0.91,Fe0.09)2SiO4); 4.85 (Fe2SiO4) |
| Optical properties | Isotropic |
| Refractive index | n = 1.8 |
| Birefringence | none |
| Pleochroism | none |
| References | [2][3][4] |
Ringwoodite is a high-pressure phase of Mg2SiO4 (magnesium silicate) formed at high temperatures and pressures of the Earth's mantle between 525 and 660 km (326 and 410 mi) depth. It may also contain iron and hydrogen. 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. In this case two hydroxide ions usually take the place of a magnesium ion and two oxide ions.[5]
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.[6][7]
This mineral was first identified in the Tenham meteorite in 1969,[8] and is inferred to be present in large quantities in the Earth's mantle.
Olivine, wadsleyite, and ringwoodite are polymorphs found in the upper mantle of the earth. At depths greater than about 660 kilometres (410 mi), other minerals, including some with the perovskite structure, are stable. The properties of these minerals determine many of the properties of the 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.
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Handbook of Mineralogy
- ^ Ringwoodite on Mindat.org
- ^ Ringwoodite on Webmineral
- ^ Ye, Y.; Brown, D.A.; Smyth, J. R.; Panero, W.R.; Jacobsen, S.D.; Chang, Y.-Y.; Townsend, J.P.; Thomas, S.M.; Hauri, E.; Dera, P.; Frost, D.J. (2012). "Compressibility and thermal expansion study of hydrous Fo100 ringwoodite with 2.5(3) wt% H2O" (PDF). American Mineralogist. 97: 573–582. doi:10.2138/am.2012.4010. S2CID 29350628. Archived from the original (PDF) on 2014-06-29.
- ^ Cite error: The named reference
sciam-oceanwas invoked but never defined (see the help page). - ^ Schmandt, Brandon; Jacobsen, Steven D.; Becker, Thorsten W.; Liu, Zhenxian; Dueker, Kenneth G. (13 June 2014). "Dehydration melting at the top of the lower mantle". Science. 344 (6189): 1265–1268. Bibcode:2014Sci...344.1265S. doi:10.1126/science.1253358. PMID 24926016. S2CID 206556921.
- ^ Binns, R A.; Davis, R. J.; Reed, No S. J. B (1969). "Ringwoodite, natural (Mg,Fe)2SiO4 Spinel group in the Tenham meteorite". Nature. 221: 943–944. doi:10.1038/221943a0. S2CID 4207095.