Vintage 18K gold plated (or gold filled) statement ring w large sparkly stone

Vintage statement ring with one large sparkly stone that is either a natural stone, or a natural crystal (but not glass as there are no inner bubbles). Size 5.75. Stamped 18 K and either GE (gold electroplated), or GF (gold filled) and has a makers mark that I can't read. The thickness of the gold layer suggests that it is, more likely, 18 karat gold filled. In preloved vintage condition, with quite a bit of wear on the gold layer, as pictured. The wear is mostly on the band and on the front edges, including prongs. Yet here is a lot of gold shine left on the inner surfaces around and behind the stone, and it still sparkles beautifully.