This is a purely theoretical question about "perfect" solids under "perfect" conditions.
Assume you have a crystalline solid with a perfect crystal lattice (i.e. no defects). Let's imagine a cube of pure diamond, perhaps 2 cm^3 in volume.
Now imagine that this solid was perfectly cleaved along a perfect single plane, with no damage to the crystal lattice on the exposed surfaces. (i.e. The cube is split into two halves, exposing two perfectly planar surfaces with no damage or loss of material.)
Furthermore, for the sake of discussion, assume that the plane of cleaving is also perfectly aligned with one of the "natural" axes of the crystal lattice.
Given these two halves of the crystalline solid, would it be possible to "reassemble" them into the original solid by perfectly aligning the two halves and pressing them together?
Given that the "cleaving" of the original solid involves breaking the inter-atomic or inter-molecular bonds holding the solid together, it seems reasonable to suggest that the solid can be reassembled by placing the two halves in their original positions, and, by exerting sufficient pressure (or energy?), cause these bonds to re-form.
In essence, we are talking about re-assembling a solid crystal without any "glue", and ending with with a single solid indistinguishable, and just as "strong" as the original.
What physical properties would prevent this from working (under ideal conditions), or is it theoretically possible? If possible, how would the required force compare to the force of cleaving? Where does the energy expended during cleaving go, and how is energy re-absorbed during re-assembly?