This is a fantastic modernist era, hallmarked sterling silver and stone ring. We think the stone is jasper. It is a mottled green that goes from a pale blueish green to a deep green. This ring is extremely heavy at 36.3 grams (more than an ounce so be prepared!). For its large size, it has a very small finger size (approx. size 5-6).
The inside diameter is 3/4" so that should help you determine how it will fit you when you compare it to the diameter of other rings you have that fit properly.
The ring is hallmarked as follows, "Handwrought Sterling" with a touchmark of the maker. The initials appear to be CS and we were unable to identify the maker.
The top of the ring measures 1 3/8" x 1" and it stands 1/2" above the shank.