Vintage Christian Dior chain with Ruby red Crystal pendant Rare Delicate gift

I took pictures of my Christian Dior chain and add a few from google old posts. I believe it is circa 1978-1980 or so It is unavailable i believe for sale. The chain is metal gold color. Not sure of content. Very pretty. Genuine.Also Poshmark requires price original but how do i know if it is from 80s So i will put formal number and how much i can part with it :)