Clueless...

[JaxHale]

Was going through some of my grandparents things and came across this pendant. I took it to a local jeweler and all they could tell me is that it looked old. It has one marking 252/81 scratched into the clasp... Anyone have any ideas?

 

[stracci2000]

Sounds like the jeweler was no help at all.
Since there are no gold marks, then it's probably costume jewelry from the 1920s-30s. The "diamond" looks like glass to me. It should be acid tested to be sure of the metal.
It's pretty, and costume jewelry from that period is desirable. Wear it and enjoy it!