Kimberlite commonly contains smectite minerals (such as montmorillonite-and saponite), which cause fragmentation or degradation of the rock when it is exposed to water or aqueous solutions. Smectites exhibit the property of interlayer cation exchange, which influences the mechanical behaviour of the kimberlite. An investigation of the influence of K+ and CU2+ cations on kimberlite revealed that K+ acts as a swelling clay stabilizer to limit breakdown of the kimberlite. In contrast, CU2+ increases the extent of swelling of kimberlite and causes rapid breakdown of the rock. The kinetics of the cation exchange reactions with these two cations was investigated. Na+ is the most readily replaced cation from the kimberlite followed by Ca2+ and K+ or Mg2+ at higher cation concentrations. (c) 2007 Elsevier Ltd. All rights reserved.