  This Article presents a nonequilibrium thermodynamic theory for the
mean-field precipitation, aggregation and pattern formation of colloidal
clusters. A variable gradient energy coefficient and the arrest of particle
diffusion upon "jamming" of cluster aggregates in the spinodal region predicts
observable gel patterns that, at high inter-cluster attraction, form
system-spanning, out-of-equilibrium networks with glass-like, quasi-static
structural relaxation. For reactive systems, we incorporate the free energy
landscape of stable pre-nucleation clusters into the Allen-Cahn-Reaction
equation. We show that pattern formation is dominantly controlled by the
Damk\"ohler number and the stability of the clusters, which modifies the
auto-catalytic rate of precipitation. As clusters individually become more
stable, bulk phase separation is suppressed.
