Very vintage Mexican sterling and amethyst ring, retailer size 4-ish

pretty sure this is an old Mexican ring, likely from the thirties. the design is unusual and lovely, the stone appears to be a pale-colored amethyst. ring is unmarked sterling, with plenty of wear but still strong. the stone wiggles a bit in the retailer bezel but can't fall out, has wear but no chips or cracks. not sure of the size, see the following...

size: measures a 3.75 but should fit a little bigger, at least a 4
height of face: 1"
width of inner band: a bit over 1/16"