- For the castle see Dragonstone (castle)
Dragonstone is a volcanic island in the Narrow Sea that guards the entrance to Blackwater Bay and the sea approaches to King's Landing, off the east coast of Westeros. It is the location of the eponymous castle of Dragonstone, the ancestral seat of House Targaryen and now seat of King Stannis Baratheon, one of the claimants to the Iron Throne.
Large amounts of dragonglass can be found on Dragonstone, but it isn't a precious or even particularly useful material, being too brittle to make weapons and too sharp to use in building. Otherwise, the only significant advantage of holding Dragonstone island is its strategic position, guarding the entrance to Blackwater Bay and King's Landing.