Methodology:

1. Sample preparation and dry crushing

Quartz (Madagascar) and alkali feldspar (Norway) samples purchased from the Geology Superstore (http://www.geologysuperstore.com) were washed with 18.2 megaohm cm-1 water and dried at 75 degrees C for over 18 hours. Minerals were then wrapped in several layers of paper roll (to avoid metal-rock interaction) and broken down using a sledgehammer on a metal plate. Crushed feldspar samples were washed again using 18.2 megaohm cm-1 water, the 63 um to 2 mm size fraction was collected and dried at 100 degrees C prior to furnacing at 450 degrees C for four hours to remove any trace organics. Quartz samples were washed using 18.2 megaohm cm-1 water, the 63 um to 2 mm size fraction was collected and dried at 100 degrees C prior to furnacing at 1000 degrees C for two hours, to remove any organics and in an attempt to remove fluid inclusions (Bray et al., 1991, Kuznetsov et al., 2012). Crushed minerals were then milled under an oxygen-free nitrogen atmosphere (zero grade, BOC), using a Fritsch Planetary Mono Mill Pulverisette 6 at 500 r.p.m. for 30 mins. Roughly 15g of sample were crushed in the ball mill at any one time. Gas samples of the ball mill headspace were taken both before and after milling the samples. This process was repeated 10 times to generate sufficient crushed sample for sacrificial incubations of the minerals. After milling, the minerals were transferred to a Coy Vinyl Anaerobic Chamber (CoyLabs, MI, US), previously flushed repeatedly with zero grade N2 until Oxoid(TM) Resazurin Anaerobic Indicator (BR0055B, Thermo Fisher Scientific Inc) indicated anaerobic conditions. Within this chamber, crushed samples were transferred into a large serum vial, which was sealed with grey butyl rubber stoppers (previously boiled in 1 M NaOH for 1 hour and rinsed 6x with 18.2 megaohm cm-1 water), and crimp sealed. The headspace of the vial was then flushed with oxygen-free-N2 for 2 mins and stored in the dark until incubation.

2. Microcosm experiments

Six x 6 g triplicate samples, one for each time point, were weighed into 50 ml borosilicate serum bottles (previously acid washed, rinsed 6 x with 18.2 megaohm cm-1 water, and furnaced at 450 degrees C for 4 hours). They were placed into an anaerobic chamber which had been repeatedly flushed with N2 until an Oxoid(TM) Resazurin Anaerobic Indicator showed that the headspace was anoxic. The serum bottles were then sealed with thick blue butyl rubber stoppers, previously boiled in 1 M NaOH for 1 hour, soaked in purite overnight and rinsed 6 times with 18.2 megaohm cm-1 water, which in turn were crimp sealed. The sealed vials were flushed for 2 mins with oxygen-free-N2 and stored at 0 degrees C until the addition of water and the start of the incubation experiments. Triplicate blank vials were prepared for each time point following the same methods. Once all vials were crimped and flushed, approximately 8 ml of 18.2 megaohm cm-1 water (flushed with N2 for over an hour) at 0 degrees C were added to each vial.

3. Headspace analysis

Serum bottles were analysed prior to the addition of water by over pressurising the bottles with 10 mL of oxygen-free N2 (zero grade, BOC). A 10 mL headspace gas aliquot was transferred into a 5.9 mL double-wadded Exetainer(R) (Labco, Lampeter, UK) using a gas-tight syringe. Approximately 8 mL of 18.2 megaohm cm-1 water (at 4 degrees C and sparged with oxygen-free N2 for over an hour) was then added to the serum bottles. The headspace in the vials was subsampled after 24 hours following the same method. Headspace samples were then taken at 48, 120, 240, 360 and 720 hours after the addition of water to the vials, following this same procedure. A 5 mL gas subsample was taken from the exetainers and analysed using an Agilent 8860 Gas Chromatograph (Agilent Technologies, Santa Clara, CA, USA). Concentrations of CH4 and CO2 were determined by a...(34)

Data collection:

List of instrumentation mentioned in methodology:

Fritsch Planetary Mono Mill Pulverisette 6 (Fritsch Milling and Sizing, NC, USA)

Coy Vinyl Anaerobic Chamber (CoyLabs, MI, US)

Agilent 8860 Gas Chromatograph (Agilent Technologies, Santa Clara, CA, USA)

Dionex ICS 6000 (Thermo Fischer Scientific, MA, US)

Gallery Automated Photometric Analyzer (Thermo Fischer Scientific, MA, US)

NOVA 1200e BET Analysis System (Aanton-Paar, Austria)

Data quality:

Concentrations of gases were calculated using a standard-curve generated from the dilution of a mixed gas standard (173738-AH-C, BOC). Standards were run daily and gave a CV of 1.0 % (n = 15) for H2, with a limit of detection (LOD) of 9.6 ppm, equivalent to 4.4 nmol g-1, a CV of 0.8 % (n = 15) for CH4, with a LOD of 0.1 ppm, equivalent to 0.04 nmol g-1 and a CV of 0.9 % (n = 15) for CO2, with a LOD of 0.1 ppm, equivalent to 0.05 nmol g-1.

Analysis of anions and organic acids, including acetate (LOD: 1.1 ppb, equivalent to 0.02 nmol g-1; CV: 1.4%), formate (LOD: 0.7 ppb, equivalent to 0.02 nmol g-1; CV: 2.3%), F- (LOD: 1.9 ppb, equivalent to 0.13 nmol g-1, CV: 8%), Cl- (LOD: 1.1 ppb, equivalent to 0.04 nmol g-1, CV: 2.6%), NO2- (LOD: 2.2 ppb, equivalent to 0.06 nmol g-1, CV: 2.2%), NO3- (LOD: 1.8 ppb, equivalent to 0.04 nmol g-1, CV: 1.9%), and SO42- (LOD: 3 ppb, equivalent to 0.4 nmol g-1; CV: 7%) and cations, including: Na+ (LOD: 0.3 ppb, equivalent to 0.50 nmol g-1; CV: 0.3%), K+ (LOD: 0.4 ppb, equivalent to 0.36 umol g-1; CV: 0.6%), Mg2+ (LOD: 1.6 ppb, equivalent to 0.26 umol g-1; CV: 1.0%) and Ca2+ (LOD: 1.1 ppb, equivalent to 0.35 umol g-1; CV: 1.1%).

Total dissolved iron (dFe): LOD of 13 ppb, equivalent to 1.58 nmol g-1.