Tiny Boulderwondrous, uncommon

This pebble appears as normal on first inspection. On closer inspection it seems as if it has excruciating detail, each little crevice and crack smaller than normal. Typically 3d6+2 Tiny Boulders are found together in a small leather pouch. As an action you can throw it 30 feet or sling it 60 feet. When the pebble strikes a surface or is crushed it rapidly expands into a large boulder. Each creature within a 5 foot radius must make a DC 15 Dexterity saving throw or take 6d10 bludgeoning damage, half on a successful save.