Vintage Jewelry Moonstone 1950s Pristine Clip-on Earrings

This was is a gift from my late mother-in-law. I have had it for at least 30 years and I believe she got it in the 1950s. There is no tarnish nor any missing parts. I have not seen a signature but the quality and workmanship of this said make it a beautiful work of art. Because it has not tarnished and all these years I am led to believe it is good metal, but I cannot say if it is Sterling. If you have information and would share it with me I would appreciate it