We present the results of simulations and theoretical
investigations of a system of particles with a weak, long-range
repulsive interaction. At fixed density the fluid phase, which is
stable at high temperatures, becomes metastable and then unstable as
the temperature is lowered. For low temperatures the particles form
approximately equal size clumps that interact weakly with
neighboring clumps. The global free energy minimum at low
temperatures corresponds to a crystalline lattice clump structure.
However the free energy surface has many minima associated with
metastable amorphous phases. Quenches from the fluid phase to low
temperatures almost always will result in an amorphous clump
structure with the number of clumps dependent on quench history. The
association of the amorphous phase with a large number of metastable
minima is similar to a mean-field spin glass.