Diamond must deform elastically under some forces, because the other two alternatives are “deforms inelastically under any forces” (i.e. not diamond) and “behaves as a rigid body under some forces” (i.e. not anything that obeys relativity).
Whether there can be a useful degree of flex, admittedly, I have no idea.
“Flexible diamond doesn’t make any sense.”
Diamond must deform elastically under some forces, because the other two alternatives are “deforms inelastically under any forces” (i.e. not diamond) and “behaves as a rigid body under some forces” (i.e. not anything that obeys relativity).
Whether there can be a useful degree of flex, admittedly, I have no idea.