  We explore the phase structure of a chiral model of constituent quarks and
gluons implementing scale symmetry breaking at finite temperature and chemical
potential. In this model the chiral dynamics is intimately linked to the trace
anomaly saturated by a dilaton field. The thermodynamics is governed by two
condensates, thermal expectation values of sigma and dilaton fields, which are
the order parameters responsible for the phase transitions associated with the
chiral and scale symmetries. Within the mean field approximation, we find that
increasing temperature a system experiences a chiral phase transition and then
a first-order phase transition of partial scale symmetry restoration
characterized by a melting gluon-condensate takes place at a higher
temperature. There exists a region at finite chemical potential where the scale
symmetry remains dynamically broken while the chiral symmetry is restored. We
also give a brief discussion on the sigma-meson mass constrained from Lattice
QCD.
