Fig. 6

Thin section photographs of sandstone samples (blue stained epoxy), showing a altered alkali feldspar showing dissolution effects (red arrow), b ferrogeneous ghost structure remains of completely dissolved alkali feldspar (red arrows), c, d authigenic, worm-like kaolinite booklets (red arrows), resulting from alkali feldspar degeneration (a Buntsandstein sandstone, Hardegsen Formation; b–d Keuper sandstone, Löwenstein Formation/Upper Burgsandstein)