The van der Waals approach to predict liquid-vapor coexistence, become
s exact in the limit of weak, long-ranged attractive forces. However,
for shorter ranged attractions, the liquid range shrinks and eventuall
y disappears altogether. When the width of the attractive well becomes
very small (less than 7% of the diameter of particles), an iso-struct
ural solid-solid transition, reminiscent of the liquid-vapor transitio
n, appears in the crystalline phase. This transition, that should be e
xperimentally observable in certain colloidal suspensions, ends in a c
ritical point. In quasi-two dimensional systems (e.g. confined colloid
s), this critical point induces the formation of a stable hexatic phas
e.