Pseudomorphoses of whewellite to weddellite reflect on transparent section preparations and in the REM appearances of cristallisation processes in the secondary whewellite formation via weddellite dehydration. As transformation products are found fine-grained polycrystalline as well as due to recrystallisation larger monocrystalline whewellite. An interesting analogy to this gives the thermic dehydration of weddellite crystals in direction to whewellite, which realises under formation of pseudomorphoses as topotactic process. The dissociation scars appearing in this case are strongly oriented to the crystal grid of weddellite.