...without learning all about geology (mafic = high Mg, Fe; low Si.... MAgnesium +FerrIC), this may help....
Serpentinite - Wikipedia, the free encyclopedia
...see reaction 2B....
~ more later?
p.s.
...although 2A is interesting... converting CO2 into methane....
uh oh.... "Reaction 2b is favored in highly magnesian compositions and low partial pressure of carbon dioxide. (Something is missing from Reaction 2b because Fe is oxidized and nothing gets reduced.)" -wiki
definetly need more later....
