This is a small and flat obsidian stone which fits into the palm of your hand. It is etched in one side with a dwarvish rune which glows white. Whilst holding the rune you may use a bonus action to trace the runic symbol with your finger to activate it. After 30 seconds (5 rounds) the rune will detonate in a large explosion, consuming the item. This explosion will create a shockwave which will destroy any stone or metal it is placed upon to a spherical radius of 5ft. All creatures within 20ft of the rune when it detonates must make a DC15 Constitution saving throw. On a failed save, take (10d6) thunder damage and become prone. On a successful save, take half damage.