Ferropericlase

Ferropericlase or magnesiowüstite is a magnesium/iron oxide with the chemical formula (Mg,Fe)O that is interpreted to be one of the main constituents of the Earth's lower mantle together with the silicate perovskite ((Mg,Fe)SiO₃), a magnesium/iron silicate with a perovskite structure. Ferropericlase has been found as inclusions in a few natural diamonds. An unusually high iron content in one suite of diamonds has been associated with an origin from the lowermost mantle.^[1] Discrete ultralow-velocity zones in the deepest parts of the mantle, near the Earth's core, are thought to be blobs of ferropericlase, as seismic waves are significantly slowed as they pass through them, and ferropericlase is known to have this effect at the high pressures and temperatures found deep within the Earth's mantle.^[2] In May 2018, ferropericlase was shown to be anisotropic in specific ways in the high pressures of the lower mantle, and these anisotropies may help seismologists and geologists to confirm whether those ultra-low velocity zones are indeed ferropericlase, by passing seismic waves through them from various different directions and observing the exact amount of change in the velocity of those waves.^[3]

Spin transition zone

Changes in the spin state of electrons in iron in mantle minerals has been studied experimentally in ferropericlase. Samples are subject to the conditions of the lower mantle in a laser-heated diamond anvil cell and the spin-state is measured using synchrotron X-ray spectroscopy. Results indicate that the change from a high to low spin state in iron occurs with increasing depth over a range from 1000 km to 2200 km.^[4][5]

Mantle abundance

Ferropericlase (Mg,Fe)O makes up about 20% of the volume of the lower mantle of the Earth, which makes it the second most abundant mineral phase in that region after silicate perovskite (Mg,Fe)SiO₃; it also is the major host for iron in the lower mantle.^[6] At the bottom of the transition zone of the mantle, the reaction

γ–(Mg,Fe)₂[SiO₄] ↔ (Mg,Fe)[SiO₃] + (Mg,Fe)O

transforms γ-olivine into a mixture of perovskite and ferropericlase and vice versa. In the literature, this mineral phase of the lower mantle is also often called magnesiowüstite.^[7]

See also

• Ilmenite
• Post-perovskite
• Wollastonite (CaSiO₃)

References

1. "Kopylova, M.G. 2006. Ferropericlase from the lowermost mantle and its geodynamic significance". Archived from the original on 2016-03-03. Retrieved 2008-03-18.
2. "Strange Blobs Beneath Earth Could Be Remnants of an Ancient Magma Ocean". Space.com. Retrieved 2018-10-01.
3. Finkelstein, Gregory J.; Jackson, Jennifer M.; Said, Ayman; Alatas, Ahmet; Leu, Bogdan M.; Sturhahn, Wolfgang; Toellner, Thomas S. (18 May 2018). "Strongly Anisotropic Magnesiowüstite in Earth's Lower Mantle" (PDF). Journal of Geophysical Research: Solid Earth. 123 (6): 4740–4750. Bibcode:2018JGRB..123.4740F. doi:10.1029/2017jb015349. ISSN 2169-9313.
4. "Researchers locate mantle's spin transition zone, leading to clues about earth's structure". Archived from the original on 2010-05-27.
5. Marcondes, Michel L.; Zheng, Fawei; Wentzcovitch, Renata M. (2020-09-25). "Phonon dispersion throughout the iron spin crossover in ferropericlase". Physical Review B. 102 (10): 104112. arXiv:2003.12348. Bibcode:2020PhRvB.102j4112M. doi:10.1103/PhysRevB.102.104112. S2CID 214693280.
6. Researchers locate mantle's spin transition zone, leading to clues about earth’s structure Archived 2010-05-27 at the Wayback Machine
7. Ferropericlase on Mindat.org