Les Amis Improbable
A Thunderstone is a rock with carvings on it that makes a loud booming noise when it is struck with a hard blow or against a surface, e.g. because it has been thrown. The noise might deafen weak creatures that are close to the source of the boom. The rock weighs 1 lb. and is quite expensive, costing 30 gp, but is one of the few reusable alchemic substances, along with fleshgems, plaster casts, and alchemical silver, that are infinitely reusable.