Comment by simias

I agree with you but I want to point out that "a traceable and immutable book" is perfectly achievable without blockchain. Just have De Beers (or the authority of your choice) publish their signed "immutable" ledger publicly at regular intervals. Anybody can mirror it (like the "nodes" of bitcoin mirror the blockchain). If the authority decides to cheat and rewrite history (for instance to change the origin of a diamond) any of the 3rd party mirrors can detect the conflict and blow the whistle.