Gerolsteiner Brunnen (Germany)

Abstract Studies of a weak sandstone which disaggregates in water reveal that particles of colloidal dimensions are released as the sand-sized particles separate. Colloids are the building blocks of gels and their presence suggests that gels (in this case silica gels) could be a component of this material. Samples of the disaggregated sandstone were collected soon after a landslide within it had occurred and, when left to stand in the ground water collected with them, naturally recemented themselves. Such behaviour implies that gels are not only present in this sandstone but also contribute to its strength. The role of gels may therefore be significant to those geohazards arising from a loss of strength.