Unusual vintage Art Deco geometric bright green glass / gemstone and silvered glass loop necklace

Very unusual vintage Art Deco necklace with large central geometric green stone and a beautiful machine age arrangement of rings made out of, I think, glass with a reflective coating. The green beads and central stone are made of a glass-like material in that they are heavy, smooth and cold to the touch. So they may well be a type of milk glass, but could be some sort of natural gemstone or mineral that I have not been able to identify.

The large glass rings are really beautiful and attach to a necklace with a fairly long overall length of 22 inches. Picture 5 shows a slight nick or scratch to the reverse of the central green stone - but this could be a natural flaw in the gemstone. This surface faces the skin so is obviously not visible when worn. Otherwise the necklace is in very good vintage condition.