Opal Marcasite Necklace Vintage

I believe this piece to be vintage. the chain is Marked FAS which is an early jewelry company which distributed from the 1970s-1990s. the pendant is stamped 925 and is 3/4ths of an inch long. it comes on a 18 inch chain. the pendant is made out of macasites and a big opal in the middle. I think it looks like a pineapple! ask me questions! make me offers!