  We construct a statistical model of crystal melting to count BPS bound states
of D0 and D2 branes on a single D6 brane wrapping an arbitrary toric Calabi-Yau
threefold. The three-dimensional crystalline structure is determined by the
quiver diagram and the brane tiling which characterize the low energy effective
theory of D branes. The crystal is composed of atoms of different colors, each
of which corresponds to a node of the quiver diagram, and the chemical bond is
dictated by the arrows of the quiver diagram. BPS states are constructed by
removing atoms from the crystal. This generalizes the earlier results on the
BPS state counting to an arbitrary non-compact toric Calabi-Yau manifold. We
point out that a proper understanding of the relation between the topological
string theory and the crystal melting involves the wall crossing in the
Donaldson-Thomas theory.
