Whimsy Unknown Blue Stone Colour Shifting Sterling Silver Ring Size R 1/2

I’ve been told this could be a type of opal as it shifts colours in the light. It’s the most electric blue when it does shift as you can see in the picture. It isn’t sea glass as glass doesn’t change colour. *This is being sold as an unknown stone.* It’s stunning and handmade. Marked as shown and has been fully tested. Size is R 1/2. 

*Preloved silver may have light surface scratches or may have tarnish*