  We propose that the amplified density fluctuations by the vanishing sound
velocity effect during the cosmological quark-hadron phase transition lead to
quark-gluon plasma lumps decoupled from the expansion of the universe, which
may evolve to quark nuggets (QNs). Assuming power-law spectrum of density
fluctuations, we investigate the parameter ranges for the QNs to play the role
of baryonic dark matter and give inhomogeneities which could affect big-bang
nucleosynthesis within the observational bounds of CMBR anisotropy. The QNs can
give the strongest constraint ever found on the spectral index.
