Examples are coffee-powder, grains, and sand on the beach or in deserts.
From the industrial point of view, storage, transport, and processing of granular matter is of eminent importance. However, scientifically speaking, the theoretical description and the understanding of the basic phenomena in granular matter are not yet satisfactory. Due to friction, elastic vibrations, and plastic deformation, energy is dissipated so that a system of granular particles is not in equilibrium and, consequently, standard methods of statistical physics cannot be applied. Continuum models do not generally work either, since the discreteness of the system is often important and rotational degrees of freedom are active, what requires enhanced theoretical approaches like the Cosserat theory. This is a difference to classical gases or fluids where systems of partial differential equations for density, momentum and energy suffice to describe the behavior properly.