The data are from a suite of friction experiments performed on 3 different grain size quartz gouges (5, 15 and 30 microns). The quartz gouge layers were sheared under a range of effective normal stresses (40-120 MPa), at a displacement rate of 1 micron/s, and the evolution of shear stress was monitored with increasing displacement (up to a maximum displacement of 8.5 mm). The gouges typically exhibit a transition from stable sliding, where the gouge layers shear in a continuous smooth fashion, to unstable sliding with displacement, where the gouges exhibit stick-slip behaviour. The transition from stable to unstable sliding occurs more efficiently in fine-grained quartz gouges and is promoted by high effective normal stresses.

Geochemical data collected during a 40 day incubation of crushed silicate minerals (quartz and alkali feldspar). Quartz and alkali were crushed separately under an oxygen-free atmosphere using a planetary ball mill. The crushed minerals where then incubated in serum vial under with oxygen-limited water, in an oxygen-free N2 atmosphere at 4 degrees C. Headspace gases were collected before the addition of water. Then, headspace gas samples and the water samples were collected 24, 48, 120, 240, 360 and 720 hours after the addition of water. Headspace gas samples were analysed for CH4, CO2 and H2 and O2. Water fraction samples were analysed for anions and organic acids (including acetate, formate, F-, Cl-, NO2-, NO3- and SO4 2-), cations (including Na+, K+, Mg2+ and Ca2+) and total dissolved iron (dFe). The research was supported by NERC grant NE/S001670/1, CRUSH2LIFE (BGO, MT, JT) and by European Research Council (ERC) Synergy Grant DEEP PURPLE under the European Union''s Horizon 2020 Research and Innovation Program (Grant Number 856416).