  In this paper, we recall various features of non equilibrium granular
systems. Clusters with specific properties are found depending on the packing
density, going from loose (a granular gas) to sintered (though brittle)
polycrystalline materials. The phase space available can be quite different.
Unexpected features, with respect to standard or expected ones in classical
fluids or solids, are observed, - like slow relaxation processes or anomalous
electrical and thermoelectrical transport property dependences. The cases of
various pile structures and the interplay between classical phase transitions
and self-organized criticality for avalanches are also outlined.
