We have studied the precipitation and growth of magnesium hydroxide Mg(OH)(2) nanopetals on zeolite 4A particles dispersed in aqueous magnesium chloride solutions at 298 K. We show that the precipitation of these petal-like nanostructures can be achieved by the addition of ammonium hydroxide to aqueous magnesium chloride, and their growth can be controlled by concentration and pH. We propose a mechanism for nanocomposite formation driven by acid-base interactions between the bridging hydroxyl groups on the zeolite surface and weakly basic Mg(OH)(2). (C) 2011 Elsevier B.V. All rights reserved.