In this article certain features of the electro-orientation effect are used to study the kinetics of coagulation in diamond colloidal dispersions. The results of a study of the influence of multivalent ions on the formation of paired aggregates from diamond particles in colloidal systems are presented. A technique was developed for studying the rate of coagulation at the early stages, using the relaxation dependences of electro-optical effects. The effect of aqueous electrolytes on the rate of formation of paired aggregates from diamond particles has been studied. It is shown that the rate of formation of paired aggregates at the isoelectric point is consistent with the theory of rapid coagulation. Based on electro-optical studies of the polarizability anisotropy of individual particles and paired aggregates from them, it was assumed that the polarizability anisotropy of a paired aggregate is lower than the polarizability anisotropy of an individual particle with volume and shape close to that of an aggregate. The rates of coagulation of colloidal systems of diamond and graphite with the same particle number concentration and size are compared. It is shown that at the isoelectric point the coagulation period of graphite colloid is five times shorter than the coagulation period of diamond colloid.