This is a lovely Kimberlite Ring. Kimberlite is a green stone that has interesting circle patterns in varying greens, browns and black colors. This ring is made with Sterling Silver. The ring is a size 6.75 and measures 1in wide by 1in tall.
Did you cut the Kimberlite from rough? I have a stone that looks fairly similar to this when cut that I found several years ago and have never been able to identify. I'm curious to see what it looks like in its pre-cabbed state.