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Figure 3. (a) Thin-sections of a tuff showing perlitic structures, micro-fractures, alteration and dissolution of minerals. The porosity is 9.11 %, and the permeability is 42.66 mD. (b) Open fracture in core, partially filled with calcite and silica. (c) Interpreted image log showing open (orange) and closed (blue) fractures and bed boundaries (green).