“…Ruiz-Agudo et al (2009) suggested that Mg 2+ inhibits etch pit spreading by its preferential incorporation as MgCO 3°a t kink/step sites in the obtuse-obtuse corners, possibly through the surface reaction with >CaOH 2 + sites. Furthermore, it has been proposed that for impurities to have significant impacts on calcite growth and dissolution processes, their concentrations must exceed certain threshold values (Fan et al, 2006;Meyer, 1984). In the present study, the solution concentrations of trace divalent cations range from $10 À1 to $10 2 ppb, which are more than three orders of magnitude lower than the impurity concentrations investigated on calcite in the literature (Arvidson et al, 2006(Arvidson et al, , 2003Astilleros et al, 2000;Davis et al, 2000Davis et al, , 2004Fan et al, 2006;Freij et al, 2005;Gutjahr et al, 1996b;Lea et al, 2001;Reeder, 1996;Ruiz-Agudo et al, 2009;Teng et al, 1999;Vinson et al, 2007;Vinson and Luttge, 2005;Wasylenki et al, 2005a, b).…”