We acquired this stunning ring as probably blue topaz but we think it may be aquamarine or pale sapphire and will change this description as needed after testing.  It may not matter to you either way, the ring is a knock out whatever it is,  but this is not the rather synthetic blue of a lot of heated blue topazes which we particularly don't like but blue topazes are a mixed bag and this needs more investigation to make a definite identification.  Meanwhile, the stone meausres 18.5 by 13.5 by 8.7mm, in a scrolled setting, mounted on a plain band, 2.9mm wide, face 24mm at widest, unmarked but testing as at least 14ct gold, size K-L, 10.0g.