Vintage large sterling adjustable black stone statement ring open band size 7.75

Vintage large oval sterling silver stamped 925, with large black shiny stone. When I purchased, ring was identified as Mexican made **possibly Taxco & stone was identified as Onyx, but I have no proof or testing if any of this info is correct, and ring is priced accordingly. Ring is heavier weight due to large oval stone and setting. Face is approximately 1 1/2" on the long side of the oval. Ring is technically adjustable: the band is open in the back and could possibly be adjusted by a professional silversmith (metal is thick, and not easily bendable). Currently sizes on the mandrel at 7.75 (I wear a size 8 and can squeeze this over my knuckle). See photos for condition and measurements. Typical vintage condition, with typical scratching, from normal wear and tear. etc. This is from my personal collection. Purging closet and jewelry items.