Gases occluded and produced from rocks

Just seven elements (Si, Al, Fe, Ca, Na, Mg, K) in oxidized form comprise 97 % of the earth s crust (Table 2.13) it is notable that silica contributes 53% of the total. With the exception of oxygen (which amounts to 46 % of all crust elements), none of such elements is in a volatile form (the only exception is SiH4). In space, carbon, nitrogen and sulfur amount to 33 % of the total abundance of material, but in the earth s crust they only constitute 0.057% (0.02%, 0.002%, and 0.035 %o, respectively). This fact of the depletion of C, N and S by about two orders of magnitude in the earth s crust shows that these elements are in partitioning among different composites. 

also known as cohenite, particularly when found mixed with nickel and cobalt carbides in meteorites (Hutchison 2007), was first identified by Ernst Wein-schenk, a German pioneer of microscopy and petrography in Munich. A general formula of cohenite is (FeNiCo)3C suggesting that this mineral also comprises the earth s core. In molten iron (above 1100°C) carbon can be dissolved up to 4.3%, about double the carbon content in cohenite (2.2%). The carbon solubility increases with temperature and when the solution slowly cools down, carbon in excess of 4.3 % separates as graphite. We have no information on carbon in the earth s core but we can speculate on it and assume that some was also mixed within other upper layers. A carbon content of 1.4-2.3 % has been found in native iron (Clarke 1920). 

We also may speculate that unstable carbides existed on the early earth and converted according to the following reactions (M = Al, Be, Ca, Na, K, Li and others)  

Similarly nitrogen can form with metal nitrides, in the form of salts of ammonia (N ) with alkali and earth alkaline metals (Na, Li, Ca, Mg etc.), as covalent compounds (with Si, P, S and others) as well as metallic carbides (with Cr, Co, Mn, U etc.), but all of them have been hydrolyzed over time in the formation of ammonia (see also next Chapter 2.2.1.3)  

M3N2 is formed from Be, Mg, Sr, Ba and Ca. Under high temperature and absence of water such nitrides can produce so-called subnitrides with the formation of nitrogen gas  

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