This ring is actually a flexible tube, hand crocheted with a small hook from fine silver wire whose ends have been attached to each other and flattened for more comfort.
Spirals of tiny black and green onyx and even tinier light green peridot beads wind all around the silver tube for a unique look.
It's 19.5 mm or a US size 9.5, but can also slightly be stretched if necessary.
Due to the flexibility of the ring it's very comfortable to wear in spite of its bold, big look.
In my opinion it looks best worn on the middle finger without any other rings.