Deposition of polydisperse An nanoclusters onto Si via condensation from toluene produces aggregates that may be structurally characterised in terms of their fractal dimension (Df). Atomic force microscopy reveals a transition (as a function of position on the sample surface) from a percolating, gel-like cluster network to isolated, low Df aggregates, highlighting the key role that local cluster concentration plays in determining the morphology of nanocluster arrays. Although the fractal dimension values measured are consistent with nucleation processes, the cluster layer morphologies bear a striking resemblance to the patterns observed following spinodal decomposition of polymer blends and binary fluid mixtures.