A simple theoretical model of magnetic-hydrophobic coagulation considering the total interaction potential energy between two spheres exposed to an external magnetic field as a sum of the van der Waals, electrostatic, magnetic, and hydrophobic components is proposed. The model was used to interpret experiments on coagulation of fine siderite particles in distilled water and 10(-2) M KCl, hydrophobized by sodium oleate. In the experiments, a relative extent of the coagulation/stability equilibrium of the siderite suspension was evaluated photoelectrically. To estimate the model parameters, the zeta-potential and hydrophobicity of siderite particles were measured. A qualitative agreement was obtained between the model predictions (energy maximum and secondary minimum) and the experimental results (voltage changes after a selected interval of sedimentation) of the siderite suspensions. Moreover, a statistically significant correlation was found between the experimental voltages and the calculated energy maximum (a crucial factor of theories on the fine particle coagulation kinetics), which can be represented by a linear regression equation with the correlation coefficient of 0.979. (C) 2003 Published by Elsevier Science B.V.