From A Wiki in the Desert
This building becomes available once you have learned the Detonation tech. To build, click on yourself and choose Projects->Misc->Detonation Box
Detonation boxes can hold up to 100 Medium Stones and up to 100 of any type of Explosives. After the materials are loaded, the option to 'Detonate Medium Stones with <Explosive>' appears.
Output depends on the type of explosive being used.