The emerald amulet is created by using a gold bar on a furnace while also carrying a cut emerald and an amulet mould. This requires 31 Crafting and grants 70 Crafting experience. The resulting unstrung amulet is then used with a ball of wool, granting an additional 4 experience.
It has no stat bonuses, but can be enchanted with the Lvl-2 Enchant spell to become an Amulet of defence which give some defensive bonuses.
Emerald amulets can be sold to Grum's Gold Exchange in Port Sarim, starting at 892 coins each if there are none in stock.