  The phase diagram of nuclear matter is quite rich - it shows such phenomena
as phase-transitions, formation of condensates, clustering, etc. From the
analysis of the spinodal instability, one can learn about the region of
liquid-gas coexistence in nuclear matter at low densities and finite isospin
asymmetries. In a recent paper, we have shown that asymmetric nuclear matter at
sub-nuclear densities should undergo only one type of instability. The
associated order parameter is dominated by the isoscalar density and so the
transition is of liquid-gas type. The instability goes in the direction of a
restoration of the isospin symmetry leading to a fractionation phenomenon.
