Dissolution and crystal growth on the (010) cleavage surface of mineral gypsum have been studied by scanning force microscopy, which allows observation of surfaces while they are in contact with aqueous solutions. Etch pits formed on the (010) surface in contact with solutions undersaturated with respect to gypsum are oriented in relation to the [001] zone axis. Edges parallel to [001] are stable or move only slowly. Edges parallel to [100] and [101] move more rapidly. Crystal growth by migration of step edges is observed in contact with supersaturated solutions. The inhibition of crystal growth by phosphonate produces gross changes in the texture of steps and terraces.