Wow, This is a beautiful ring with medium to dark brown ironstone laced with lots of sparkling opal predominately  green with gold and the occasional flicker of purple/blue. More sparkle than shows in the photos. Opal measures approx 26mm x 17mm.  (including setting is 31mm x 23mm)  Inside diameter of ring is 20mm x 17mm.  Ring size approx US 5.5