Figure 13b: Surface charge developing on an olivine crystal during the 1st heating/cooling in the N2-CH4 gas mixture. In contrast to the first heating in pure N2, when the positive surface dissipates after cooling, heating in the N2- CH4 gas mixture leaves a positive surface charge. The colors correlate with ΔT ranges at which the bulk polarization of the olivine crystal is affected by the reaction with CH4.