Formation of H2 and CH4by weathering of olivine at temperatures between 30 and 70°C

Table 2 Rates of olivine dissolution and CH₄ accumulation

pH	Initial fluid composition	Grain size (m)	Temp (°C)	Duration of dissolution (days)	Dissolution rate based on Si (Mg) (mol/m²/s)	Accumulation rate of CH₄ (mol/m²/s)
8.72	2.2 mM HCO^-₃	2.5E-4 to 1E-4	30	295	8.10E-12 (7.28E-12)	2.70E-11
8.74	2.2 mM HCO^-₃	2.5E-4 to 1E-4	50	295	1.81E-11 (4.68E-12)	3.21E-11
8.57	2.2 mM HCO^-₃	2.5E-4 to 1E-4	70	295	5.12E-11 (1.91E-12)	7.31E-11
9.05	H₂O (Milli-Q)	2.5E-4 to 1E-4	30	295	6.35E-12 (5.46E-12)	2.73E-11
9.01	H₂O (Milli-Q)	2.5E-4 to 1E-4	50	295	1.46E-11 (7.41E-12)	3.12E-11
9.09	H₂O (Milli-Q)	2.5E-4 to 1E-4	70	295	6.39E-11 (1.79E-12)	5.39E-11

Rates of dissolution calculated from the release of Si and Mg into solution and from the accumulation of CH₄ into the headspace of the experiment bottles after 295 days of dissolution. The CH₄ rate is calculated from the net accumulation of CH₄ into the headspace of the bottles, i.e. with the control values subtracted from the analyzed values. The pH is changing between the buffered and non-buffered groups but not remarkably within the groups.

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