Vintage Mexican sterling silver signet ring. It is set with a brilliant art glass stone that they has been called a paper opal or a foiled opal. It has an uneven surface and one chip that you can see as a white mark in some of the photos. The stone is so bright that I could not bear to send this to melt. 

Size 7 and measures 1/2" wide. Weight: 5.6 grams. Marked 925.