Emerald

Ironman verdict

At least 6 monsters drop it. The easiest is Goblin statue (level 70, 40/602); the best rate is Dragonstone dragon (level 119), at 10/128, about one every 3 kills. You can also make it yourself: it takes 27 Crafting and gives 67.5 Crafting XP, using Uncut emerald. Other sources include Earth impling, Earth impling jar, Thalassus and Casket (Pirate's Treasure), plus 4 more listed below. Making ten takes 10 × Uncut emerald and gives 675 Crafting XP. Reaching level 27 Crafting takes 9,730 XP in total; the Crafting calculator counts the actions and materials to any target, and the Crafting guide has the Ironman training route. 11 recipes use Emerald, including 'Forged in War' sculpture, Animate Rock scroll (One of a Kind) and Blurite keystone. Emerald is available on free-to-play worlds too. It is tradeable on normal accounts, but an Ironman cannot use the Grand Exchange or trade for it, so the sources on this page are the whole list. High Alchemy turns one into 300 coins, which is 200 less than the shop price, so buying it to alch does not pay.