H 2 generation in wet grinding of granite and single‐crystal powders and implications for H 2 concentration on active faults

Granite and single crystals of quartz, alkali feldspar, biotite and muscovite are ground in pH‐controlled and pure water solutions using a ball mill at ambient condition to examine the production of H 2 . The amount of H 2 generated by grinding is linearly related with the surface area of ground samples. The slope of the straight line indicates H 2 productivity of each mineral: 3.9 × 10 −3 μmol/m 2 (quartz); 1.0 × 10 −3 μmol/m 2 (alkali feldspar); 3.6 × 10 −2 μmol/m 2 (biotite); 2.2 × 10 −2 μmol/m 2 (muscovite); 4.5 × 10 −3 μmol/m 2 (granite). High productivity of biotite and muscovite is probably related to the existence of hydroxyls in their crystal structures. Interestingly, H 2 production did not depend on the pH of the solution in the case of biotite and granite, while comparisons between fluid acidity and H 2 concentration on several active faults suggest that anomalously high H 2 is commonly observed at relatively acidic water springs. This correlation may be explained by locally high abundance of phyllosilicates.