Dragonstone is a removed unobtainable material that was found in the player's base next to the Marketplace during the Medieval Event. It could only be mined with a Dragonglass Pickaxe, and gave 1000 EXP upon mining. 16 Dragonstone ores would appear each rejoin, so it was somewhat effective for low rank grinding. It's only usage was as a path obstacle for the Helen Quest.
Dragonstone has since been removed as of the 2017 Halloween update, however it's emblem remains in the shop for some reason.