  We present a phenomenological theory of nuclei which incorporates clustering
at the nuclear surface in a general form. The theory explains the recently
extracted large symmetry energy at low densities of nuclear matter and is
consistent with the static properties of nuclei. In phenomenological way
clusters of all sizes, shapes along with medium modifications are included. The
importance of quartic term in symmetry energy is demonstrated at and below the
equilibrium density in nuclear matter. It is shown that it is related both to
clustering as well as to the contribution of three-nucleon interaction to the
equation of state of neutron matter. Reasons for these are discussed. Due to
clustering the neutron skin thickness in nuclei reduces significantly.
