- "The door and the vault is made of Valyrian stone. The hardest stone does not make a mark."
- ―Xaro Xhoan Daxos
Valyrian stone is a hard type of stone, originating from Valyria. It is apparently harder than any other known type of stone.
Xaro Xhoan Daxos shows Daenerys Targaryen his vault, stating that both the inside and the door are made from Valyrian stone. He also says that he offered the best locksmiths in Qarth their weight in gold if they could break into it, however, they all walked away empty handed. Xaro later offers its contents if she consented to his marriage proposal. Xaro keeps the key to the vault in the form of a necklace.
After defeating Pyat Pree, Daenerys returns to the vault, along with the captured Xaro (now the self-proclaimed King of Qarth) and his lover (Daenerys's handmaiden Doreah), and opens it, revealing nothing. She later locks both Xaro and Doreah in the vault for their betrayal.
In the books
In the A Song of Ice and Fire novels, there is no mention of a material called Valyrian stone, but instead one called dragonstone. It is similar to the mysterious oily black stone, albeit dry. Dragonstone, the dragonroads, Tyrosh's inner walls, the Black Walls of Volantis, and Valyrian ruins in Naath are all made of dragonstone. The material is harder than even diamond, thus it is extremely difficult to work it. The Valyrians apparently used magic to work it.