Fig. 2: Illustrations of glass transformation into alteration products.

a Representation of a cross section of an altered piece of glass. The alteration layer is generally made up of a hydrated layer (also called ‘interdiffusion’ or ‘leached’ layer), the gel layer (amorphous hydrated polymerized Si-rich material) which can be made of several sub-layers depending on how it forms, and secondary phases (precipitates). b Scanning electron microscopy image of a piece of SON68 glass, a 30 oxide borosilicate glass (Table 1), altered for 2 months at 150 °C in deionized water. The sample was broken and observed from the edge. Secondary phases precipitated on the top of the gel layer consist of poorly crystallized phyllosilicates. c Transmission Electron Microscopy bright field image of a SON68 glass sample (composition given in Table 1) altered for 26 years at 90 °C in granitic water. Pores within the gel can be seen in bright.