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 H2. The amount of H2 generated by grinding is linearly related with the surface area of ground samples. The slope of the straight line indicates H2 productivity of each mineral: 3.9 ¿ 10-3 ¿mol/m2 (quartz); 1.0 ¿ 10-3 ¿mol/m2 (alkali feldspar); 3.6 ¿ 10-2 ¿mol/m2 (biotite); 2.2 ¿ 10-2 ¿mol/m2 (muscovite); 4.5 ¿ 10-3 ¿mol/m2 (granite). High productivity of biotite and muscovite is probably related to the existence of hydroxyls in their crystal structures. Interestingly, H2 production did not depend on the pH of the solution in the case of biotite and granite, while comparisons between fluid acidity and H2 concentration on several active faults suggest that anomalously high H2 is commonly observed at relatively acidic water springs. This correlation may be explained by locally high abundance of phyllosilicates.