Smooth basal plane and edge surfaces of two platy phyllosilicate minerals (muscovite and talc) were prepared successfully to allow accurate colloidal force measurement using an atomic force microscope (AFM), which allowed us to probe independently interactions of divalent cations with phyllosilicate basal planes and edge surfaces. The Stern potential of basal planes and edge surfaces was obtained by fitting the measured force profiles with the classical DLVO theory. The fitted Stern potential of the muscovite basal plane became less negative with increasing Ca2+ or Mg2+ concentration but did not reverse its sign even at Ca2+ or Mg2+ concentrations up to 5 mM. In contrast, the Stern potential of the muscovite edge surface reversed at Ca2+ or Mg2+ concentrations as low as 0.1 mM. The Stern potential of the talc basal plane became less negative with 0.1 mM Ca2+ addition and nearly zero with 1 mM Ca2+ addition. The Stern potential of talc edge surface became reversed with 0.1 mM Ca2+ or 1 mM Mg2+ addition, showing not only a different binding mechanism of talc basal planes and edge surfaces with Ca2+ and Mg2+, but also different binding mechanism between Ca2+ and Mg2+ ions with basal planes and edge surfaces. (C) 2013 Elsevier Inc. All rights reserved.