This is an exquisit Art Deco ring made of onyx and marcasites set in silver.  The face of the ring is a rectangle 7/16" (11mm) wide by 7/8" (22mm) long.  Three long bars of prong set faceted onyx are lined-up in a slanted pattern surrounded by bead set marcasites.  The shoulder of the ring also has a nice taper with bead set marcasite.  It is marked "Sterling" and has a symbol of what appears to be a horned animal, perhaps a bull, with the number "3" inscribed within.   I have not yet found the identity of this mark although it does resemble the type of markings used by Mexican silver shops.  The styling of this ring with it's rectangular face and geometric stones is softened by the swirling pattern of the marcasite setting.  This ring just screams 1930s and is a real treasure from the Art Deco period.  In excellent condition, it is a size 7.   SORRY! THIS ITEM HAS ALREADY BEEN SOLD.

View of shoulder: