Fig. 3: SEM images of the original albite (basalt) and its recovered products after different PT treatments.

Mid-IR spectra from respective samples are shown as inset images. a The original anhydrous albite is characterized by its prismatic crystal habits and featureless IR spectra (upper inset) whereas b the recovered product under 1:1 albite-to-water ratio shows the characteristic clay crystal habits and the IR band (upper inset) by NaOH at 3587.8 cm⁻¹ (ref. ²⁷). The O–H stretching mode of the hydrated Na-smectite is also identified as a broad band at 3484 cm⁻¹. c A representative SEM image and XRD pattern (upper inset) of the recovered product using 6 wt.% H₂O from 2.4 GPa and 260 °C conditions (see Supplementary Fig. 2 for data using different water contents). d A representative SEM image of the original natural basalt (starting material). e A representative SEM image of the recovered basalt sample from 2.5 GPa and 250 °C under wet condition by 5.5 wt% H₂O. f A representative SEM image of the recovered basalt sample from 2.5 GPa and 250 °C under dry condition. Phase abbreviations: alkali-feldspar: Afd; plagioclase: Pl; clinopyroxene: Cpx, augite; and ilmenite: Ilm.