As the concentration of silico tungstate particles (SiW12O404-) is increased at fixed background electrolyte concentration, the suspension separates into a dense, crystalline colloidal phase in equilibrium with a dilute colloidal liquid. The solubility of the particles ranges from 2.67 to 0.2 g/mL as the background 1:1 electrolyte concentration increases from 0 to 5 M. The second virial coefficient of suspensions of silicotungstate particles is a decreasing function of electrolyte concentration and, if interpreted in terms of square well or adhesive hard sphere pair potentials, suggests the particles’ feel attractions are on the order of 0-2kT at the phase boundary. Despite attractions of sufficient strength, colloidal gas/colloidal liquid phase transitions are not observed. These results are interpreted as indicating particles feel an attraction with an extent which is much smaller than the core particle diameter.