First of all thanks a lot! I think I'll find enough references based on your comments (I cannot use a forum post as a reference).
Blockchain can help in achieving trust in the origin of a diamonds (e.g. it's not a blood diamond) since it is to be able to digitally track a diamond’s journey from mine to a consumer in a tamper-proof way. The literature criticizes that there is no way of achieving physical trust by blockchains since there is no "real" connection between the data stored in a blockchain and the real world goods. My argument is that for diamonds this is not the case since every diamond is unique and thus once the metadata (the unique properties of a diamond) and the respective certificates are stored in the blockchain there is no way to replace a diamond in a later stage of a supply chain.
So it's more about proving the real origin of a diamond. I just needed an argument that it's verifiable that a diamond entered in the first step of a blockchain cannot be replaced at a later stage.
If you're interested in this topic I would recommend you to have a look at Everledger, a startup that is using the blockchain technology to improve the diamond supply chain.
Here are some interesting articles and papers: