## 4 Results  
### Petrographic and Chemical Characterisation of Rocks before and after SC CO\({}_{2}\) Exposure  
The two lithologies (CG and GD) used in experiments and tested as described above show similar textural and mineralogical results. After interaction of the rock specimens with the SC CO \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Rock Composition** & **Vol. Fraction (\%)** & \multicolumn{2}{c}{**10 cm\({}^{2}\)/g**} & **75 cm\({}^{2}\)/g** & **120 cm\({}^{2}\)/g** & **170 cm\({}^{2}\)/g** & **220 cm\({}^{2}\)/g** \\ \cline{3-6}  & & & & **Reactive Surface Area (m\({}^{2}\)/m\({}^{2}\))** & **(or**\(A_{\text{initial}}\))** & \\ \hline Albite, NaAlSi\({}_{\text{O}}\)\({}_{\text{O}}\) & 0.35 & 9.15 & 68.65 & \(1.09\times 10^{2}\) & \(1.55\times 10^{2}\) & \(2.01\times 10^{2}\) \\ Anorthite, CaAl\({}_{5}\)Si\({}_{\text{O}}\)\({}_{\text{S}}\) & 3.25 & 88.32 & \(6.62\times 10^{2}\) & \(1.06\times 10^{3}\) & \(1.5\times 10^{3}\) & \(1.94\times 10^{3}\) \\ Diopside, CaMgSi\({}_{\text{O}}\)\({}_{\text{O}}\)\({}_{\text{S}}\)\({}_{\text{O}}\) & 10.8 & \(3.53\times 10^{2}\) & \(2.64\times 10^{3}\) & \(4.23\times 10^{3}\) & \(5.9\times 10^{3}\) & \(7.76\times 10^{3}\) \\ Forsterite, Mg\({}_{\text{S}}\)SiO\({}_{\text{O}}\) & 2.42 & 77.1 & \(5.78\times 10^{2}\) & \(9.25\times 10^{2}\) & \(1.31\times 10^{3}\) & \(1.69\times 10^{3}\) \\ Fayalite, FeSiO\({}_{\text{A}}\) & 2.21 & 96.63 & \(7.24\times 10^{2}\) & \(1.16\times 10^{2}\) & \(1.64\times 10^{3}\) & \(2.12\times 10^{3}\) \\ Enstatite, MgSiO\({}_{\text{S}}\) & 0.56 & 19.97 & \(1.34\times 10^{2}\) & \(2.15\times 10^{2}\) & \(3.05\times 10^{2}\) & \(3.95\times 10^{2}\) \\ Ferrosilite, FeSiO\({}_{\text{S}}\) & 0.41 & 16.0 & \(1.2\times 10^{2}\) & \(1.92\times 10^{2}\) & \(2.72\times 10^{2}\) & \(3.52\times 10^{2}\) \\ \hline \(\Phi\) (brine fraction) & 80 & & & & & \\ \hline Total & 100 & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Considered modal composition assumed for cumulate gabbro modelling and reactive surface area considered for the calculations. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Components** & **(mg kgw\({}^{-1}\))** & **(mol kgw\({}^{-1}\))** \\ \hline Ca\({}^{2+}\) & 2050 & \(5.12\times 10^{-2}\) \\ Mg\({}^{2+}\) & 560 & \(2.33\times 10^{-2}\) \\ Fe\({}^{2+}\) & 5.16 & \(1.01\times 10^{-4}\) \\ SiO(\({}_{\text{O}}\))(\({}_{\text{O}}\)) & 11.5 & \(1.55\times 10^{-4}\) \\ K\({}^{+}\) & 260 & \(6.64\times 10^{-3}\) \\ Na\({}^{+}\) & 85,450 & 3.7 \\ SO\({}_{4}^{2-}\) & 5400 & \(5.62\times 10^{-2}\) \\ Cl\({}^{-1}\) & 133,500 & 3.56 \\ \hline \hline \supersaturated brine in the autoclave chamber, an increase in the dissolution of specimens can be perceived; after the one-day run there is a noticeable surface roughness, which increases for the longer runtimes and eventually leads to material fragmentation for 16-day and 64-day runs (Figure 3). The mean linear roughness (Ra) is higher on CG from 14.80 \(\upmu\)m to 21.89 \(\upmu\)m for 16 and 64 days, respectively, whereas for GD the Ra increases from 1.01 \(\upmu\)m to 1.85 \(\upmu\)m for 16 and 64 days, respectively. The petrographic analyses, through transmitted light microscopy, did not show significant mineralogical or textural differences after the experiments. It is important to note that even if there were any changes, they should be located on the surface and the thin section production process could have eliminated them. The powder-XRD performed on global fraction before immersion [11] reflects the modal igneous composition given by clinopyroxene, olivine, amphibole, plagioclase and magnetite for CG and plagioclase, clinopyroxene, olivine and mica for the GD (Table 4). Clinochlore has been identified on both rock samples and probably derived from the alteration of the mafic mineralogical phases. After the 1-, 4-, 16- and 64-day runs, the obtained powder diffractograms (Table 4) shows besides the igneous mineralogy the new presence of talc, vermiculite, and halite on both CG and GD in most specimens.