  We study the amplitude modulation of ion-acoustic wave (IAW) packets in an
unmagnetized electron-ion plasma with two-temperature (cool and hot) electrons
in the context of the Tsallis' nonextensive statistics. Using the
multiple-scale technique, a nonlinear Schr{\"o}dinger (NLS) equation is derived
which governs the dynamics of modulated wave packets. It is shown that in
nonextensive plasmas, the IAW envelope is always stable for long-wavelength
modes $(k\rightarrow0)$ and unstable for short-wavelengths with $k \gtrsim1$.
However, the envelope can be unstable at an intermediate scale of perturbations
with $0<k<1$. Thus, the modulated IAW packets can propagate in the form of
bright envelope solitons or rogons (at small- and medium scale perturbations)
as well as dark envelope solitons (at large scale). The stable and unstable
regions are obtained for different values of temperature and density ratios as
well as the nonextensive parameters $q_c$ and $q_h$ for cool and hot electrons.
It is found that the more (less) the population of superthermal cool (hot)
electrons, the smaller is the growth rate of instability with cutoffs at
smaller wave numbers of modulation.
