u/Healthy-Use-6397

I recently inherited my grandmothers jewelry. I found a choker/collar style necklace with Cartier stamping on it as well as what appears to be a serial number. I was told it would have been something she would have maybe worn in the 60s-70s.
I can’t find anything like it online. Where can I go, or who can I go to for some help identifying it?