Agglomeration of monodisperse thiol-stabilized gold particles with diameters of 6 nm, suspended in organic solvents, was induced by the cooling of the suspension. A sharp transition between the stable suspension and agglomeration resulted. The temperature of the transition depends on the concentration and the compatibility of the solvent. The morphology of the formed particle structures upon agglomeration implies that the used metal colloid can be described as a van der Waals-gas. The particles undergo phase transitions from a stable fluid phase to a metastable phase, in which nucleation and growth occur, or to an instable phase, in which spinodal decomposition occurs. The results will direct research on routes to nanostructured materials using nanoparticles as building blocks.