That's a nice find ! I think it's pretty modern though based on the .925 (rather than Sterling designation ) and while the marcasites
are indeed a nod to an earlier time (1910 /20's ) the style of the flat black heart is really a more modern touch . It may well be resin
not onyx or stone . Obviously these are my remote opinions based on a couple of pictures - and it is a very nice find even if modern !