Why re-invent the wheel? Sounds to me like ecash would be the right tool for the job. You can mint whatever you want, including gems.
(Please correct me if I'm wrong nostr:nprofile1qqs9pk20ctv9srrg9vr354p03v0rrgsqkpggh2u45va77zz4mu5p6ccpzemhxue69uhk2er9dchxummnw3ezumrpdejz7qgkwaehxw309a5xjum59ehx7um5wghxcctwvshszrnhwden5te0dehhxtnvdakz7qrxnfk)