Vintage pre-WWII Edwardian German locket necklace. The front has a nice design and blue stone (I think it is a rhinestone, but it may be something else). The inside is marked KJ with an arrow for Kollmar & Jourdan (based in Pforzheim).
The chain has one odd link in it. The charm and chain show some wear / discoloration. The locket opens from the top.
Necklaces like this have been common in Germany since WWI. The last photo is from a late 1910s Prym catalog (Prym's Zukunft Die Weltmarke Verzeichnis der Zugabe Artikel).