This is an extraordinarily beautiful vintage Art Deco ring. It has a large oval onyx stone with a diagonal stripe of malachite inlaid into it. It is set in a 14K white gold filigree setting with exceptionally nice detail. It also features a small diamond set in the upper quadrant of the face.
It is marked PS Co for the Plainville Stock Company of Massachusetts. They began making jewelry in the late 19th century and their 1927 trade directory lisitings indicate that they were making 14K, 18K and platinum rings as well as other pieces.
The ring is a size 4 (a little on the larger side of this). The face of the ring measures about 7/8 inch north to south and about 1/2 inch across. It is in very good condition with some light wear. The stone is a little loose, but in no danger of falling out.