MOSCOW, August 1. /TASS/. An international group of scientists from Russia, France, Germany, Italy, and the US researched the properties of iron carbonates under high temperature and pressure conditions and came to the conclusion that these substances might play an active role in the formation of diamonds, Skoltech’s press office said. The results of the study were published in the scientific journal Nature Communications.
The Earth's deep mantle is characterized by especially severe conditions: the high pressure of more than one million times the normal atmospheric pressure and temperature of about 2,200 degrees Centigrade. Most chemical compounds that are stable on the Earth's surface cannot exist under such extreme conditions. The scientists found out this behavior under such conditions by the carbonates, carbon-containing substances, which are very abundant in the Earth's mantle, and which can be found as an inclusion in deep diamonds.
The scientists, including a research assistant from the Skoltech Center for Hydrocarbon Recovery, simulated the conditions under which the substances at the depth of Earth's mantle exist. Extreme pressure and temperature were generated by means of laser-heated diamond anvil cells. Very small crystal samples (10 to 15 microns) were squeezed between a pair of diamonds with a laser beam focused on them. The structure of samples has been further analyzed with synchrotron X-rays.
The researchers discovered that under extreme conditions, the structures of carbonates is reorganized so that the carbon carries an extra oxygen atom, forming a tetrahedral shape. In total, they found two new compounds including modified carbonate which has the potential to survive deep in the Earth’s lower mantle. The reaction of the iron self-oxidation enables the carbonates to survive in the Earth's mantle down to such a depth that they might be able to participate in forming diamonds.
The obtained results demonstrate the capability of existing absolutely new crystal structure with exceptional stability which is important to be the part of the diamond formation process.