I realise it's a crystal lattice, but the diagrams merely show the edges going on forever, how diamonds have fixed shapes, what happens at edges? Surely there aren't just carbon bonds floating around.
4tran, help me out here. If your option "c" was true, then a microscopic portion of the diamond would transform from the hardest substance to the softest. Even being so small, that soft substance could be abraded off. That leaves danglers, which become more graphite, and then the process repeats. That suggests that diamonds would disintegrate into graphite (or graphite flaws destroy the diamond). That doesn't seem to happen with diamonds that are worked (as industrial diamonds in drill bits, etc.) such that they would reveal such a process.