The Emerald ring is made by using a gold bar on a furnace whilst having an emerald and ring mould in the inventory. It requires a Crafting level of 27 and gives 55 experience when made.
They are dropped by crawling hands and can also be obtained from bird nests. The ring has no stats but can be enchanted using level 2 enchant (27 magic) to make a ring of dueling.
Emerald rings can be sold to Grum's Gold Exchange in Port Sarim, starting at 892 coins each when none are in stock.
Obtaining steel, iron or silver keys from H.A.M. Guards gives you a chance to get jewellery ranging from sapphire to diamond.