Heterocoagulation in suspensions containing both aluminum hydroxycarbonate and magnesium hydroxide leads to the development of an aluminum hydroxycarbonate coating on the magnesium hydroxide particles. For this reason, mixed suspensions exhibit isoelectric points similar to those of aluminum hydroxycarbonate, but markedly different from magnesium hydroxide. The finding is significant in relation to physical properties of the systems as mixed suspensions demonstrated rheological behavior which responded to changes in media pH in a manner analogous to aluminum hydroxycarbonate suspensions. Thus, a maximum yield value of the mixed suspension was observed at a pH corresponding to the isoelectric point of the aluminum hydroxycarbonate coating.