  We give a strong evidence that noncrystalline materials such as quasicrystals
or incommensurate solids are not exceptions but rather are generic in some
regions of a phase space. We show this by constructing classical lattice-gas
models with translation-invariant, finite-range interactions and with a unique
quasiperiodic ground state which is stable against small perturbations of
two-body potentials. More generally, we provide a criterion for stability of
nonperiodic ground states.
