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This chapter reviews the distribution of carbon-bearing phases in the crust, mantle, and the core. It presents conditions of stability of various carbon-bearing phases - such as carbonate minerals, carbon-bearing fluids, graphite, diamond, and carbides - and how these stabilities put limits on the carbon budget of the mantle. The chapter also discusses expectations about how stability may have varied throughout geologic time, given the thermal and redox evolution of the Earth. Finally, this chapter also presents recent discoveries about carbon mineral evolution.

The combined luminescence and Raman-scattering microspectroscopy technique allows separate spectroscopic studies on several crystal phases in mixed compounds. A mixed sample of LiBaAlF6 and Ba3Al 2F12 doped with Pr was studied. The Pr3+ concentration was found to be much higher in the Ba3Al 2F12 phase. Several non-equivalent Pr3+ centers are present in both compounds, however, only in Ba3Al 2F12 there are several non-equivalent crystallographic positions of Ba. In LiBaAlF6 non-equivalent Pr3+ centers appear because of complicated scheme for charge compensation of ( PrBa3+)+. Possible reasons of Ba3Al2F 12 formation in the process of Pr3+:LiBaAlF6 growth are discussed. An excess of LiF in melt is assumed to produce ( LiBa+)- antisite defects as a charge compensation for ( PrBa3+)+ substitution. © 2013 Elsevier Ltd. All rights reserved.

The combined luminescence and Raman-scattering microspectroscopy technique allows separate spectroscopic studies on several crystal phases in mixed compounds. A mixed sample of LiBaAlF6 and Ba3Al 2F12 doped with Pr was studied. The Pr3+ concentration was found to be much higher in the Ba3Al 2F12 phase. Several non-equivalent Pr3+ centers are present in both compounds, however, only in Ba3Al 2F12 there are several non-equivalent crystallographic positions of Ba. In LiBaAlF6 non-equivalent Pr3+ centers appear because of complicated scheme for charge compensation of ( PrBa3+)+. Possible reasons of Ba3Al2F 12 formation in the process of Pr3+:LiBaAlF6 growth are discussed. An excess of LiF in melt is assumed to produce ( LiBa+)- antisite defects as a charge compensation for ( PrBa3+)+ substitution. © 2013 Elsevier Ltd. All rights reserved.

Helium is generally understood to be chemically inert and this is due to its extremely stable closed-shell electronic configuration, zero electron affinity and an unsurpassed ionization potential. It is not known to form thermodynamically stable compounds, except a few inclusion compounds. Here, using the ab initio evolutionary algorithm USPEX and subsequent high-pressure synthesis in a diamond anvil cell, we report the discovery of a thermodynamically stable compound of helium and sodium, Na 2 He, which has a fluorite-Type structure and is stable at pressures >113â €..GPa. We show that the presence of He atoms causes strong electron localization and makes this material insulating. This phase is an electride, with electron pairs localized in interstices, forming eight-centre two-electron bonds within empty Na 8 cubes. We also predict the existence of Na 2 HeO with a similar structure at pressures above 15â €..GPa. © 2017 Macmillan Publisher Limited part of springer Nature. All rights reserved.