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New information on the Earth’s mantle from outer space

Thanks to a mineral discovered in a meteorite

How did our planet evolve over the billions of years of its history and what are the characteristics of its core and mantle? The answer is contained in a small fragment of meteorite, inside which the international research team lead by Luca Bindi, a professor at the Department of Earth Sciences, has identified a new mineral named hiroseite. This is reported in a study published in the journal Science Advances providing the first ever experimental confirmation of the hypotheses made on the transformations occurred in the composition of our planet since its formation.


The new mineral, an iron and magnesium silicate, was identified in a sample of the Suizhou meteorite, which fell in 1986 in Dayanpo, China. The pressure and temperature in which the hiroseite was formed, in the collision between asteroids in space, are comparable to those present in the deep mantle of our planet and in its composition there is a high presence of oxidized iron, a state of the chemical element hitherto only hypothesized in this layer of the Earth. 


“To understand the meaning of this discovery,” comments Bindi, professor of Mineralogy of the University of Florence, “it is necessary to start from the fact that iron can exist in three oxidation states, metallic iron (Fe0) and iron in the bivalent form Fe2+ and trivalent Fe3+; the latter two are formed in contact with oxygen, just as it happens in the process of rusting. It is thought that only iron in the metallic state exists in the Earth’s core while in the mantle, the scientific community believes that the iron is present as Fe2+ and Fe3+.”


In addition to describing the new mineral species, thanks to the chemical and structural study of Hiroseite, the Florentine researcher and colleagues from Arizona State University and the Guangzhou Institute of Geochemistry (the Chinese Academy of Sciences) were able to experimentally demonstrate the hypothesized mechanism  responsible for the oxidation of our mantle, clarifying that oxidized Fe is formed directly in the mineral itself, as in the specimen they identified.


The new mineral, whose name is dedicated to Kei Hirose, the Japanese geophysicist who has studied for years the possible minerals present in the great depths of our planet, will also allow scientists to get closer to understanding the composition of the Earth's core.

14 January 2020
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