Mexican Cantera Opal Ring in Sterling Silver Size 5 3/4

Vintage Mexican sterling silver ring with orb decoration. It is set with a Mexican Cantera opal that has pale beige matrix and clean opal with colorful play of color. The ring has been worn and the surface of the stone has scratches. It also has a horseshoe shaped nick that is polished out which tells me that the lapidary expert made it this way. It is not damage. 

Ring is a size 5 3/4 and measures 1 1/8" long. Hallmarked on the back. Weight: 5.5 grams. Silver has tarnish. 

Here it is in the sun: