Black Opal & Diamond Cocktail Ring, circa 1950's to 60's

I'd place this Lightning Ridge black opal ring circa late 1950's to 1960's, probably in the era of the "cocktail ring". It's stamped 18ct and has a white gold top, most likely made in the UK or possible Australia.

The Lightning Ridge black opal is just over 11 x 9mm, about 2.5ct, surrounded by 16 brilliant cut diamonds. The play of colour shows in neon green stripes that catch the light in different angles, it's an unusual stone.

This is another example of true black N1 body tone, and I've shown a pic of the back so you can see just how black it really is. I'll post a clickable link to the opal body tone chart in the first comment below so you can see what N1 and the other body tones look like.