Weathering of sandstone by alunogen and alum salts

In many places in eastern Germany, the Czech Republic and southern Poland, outcrops of the Elbsandstein are undergoing rapid honeycomb weathering and scaling in the presence of gypsum, alunogen and alum salts. Laboratory experiments have been undertaken to test the relative efficacy of these salts as weathering agents. Cubes of Lower Cretaceous sandstone from West Sussex have been repeatedly soaked in salt solutions and then oven dried at 50°C. The experiments show that alunogen causes relatively little damage, but alum salts are highly destructive, especially if gypsum is present. The addition of gypsum reduces the damaging effects of alunogen, while gypsum on its own causes minimal weathering.