Two of the stamps are very very hard to get a clear image of, but there is (GNG)(OK (WITH A SYMBOL TO THE RIGHT) ) , and (10k( with a symbol to the left slightly slightly in the recess) ) . I will try to get a clear(ER) image , also has 7 small stones in the channel on top of the ring.And I thought finding $8 in change in a new-used car was fun!
I wonder if you could trace to the previous owner...see if they lost a piece of jewelry.
But that might just open a can of worms.
Sorry to not be more helpful about identifying it. The hallmark is hard to read. Is it possible to get a crisper image?