Experimental weathering of sandstone by combinations of salts

Laboratory experiments are described that examined the effectiveness of certain naturally occurring combinations of salts as weathering agents. Cubes of a highly quartzose sandstone were repeatedly soaked in one of a series of salt solutions and then oven-dried to simulate natural weathering. The weathering effect of both potassium alum and ammonium alum is enhanced by the presence of alunogen or gypsum whereas sodium chloride depresses the effect of the alums. Sodium chloride combined with gypsum is confirmed as appreciably more destructive than either of the salts alone. The results indicate that it is difficult to predict the weathering behaviour of combinations of salts from the weathering behaviour of the salts individually. Possible causes of enhanced weathering by some combined salt solutions are discussed.