Explosive antimony

Explosive antimony is an allotrope of the chemical element antimony that is so sensitive to shocks that it explodes when scratched or subjected to sudden heating. The allotrope was first described in 1855.
Chemists form the allotrope through electrolysis of a concentrated solution of antimony trichloride in hydrochloric acid, which forms an amorphous glass. 
This glass contains significant amounts of halogen impurity at its boundaries. 
When it explodes the allotrope releases of energy per gram. White fumes of antimony trichloride are produced and the elemental antimony reverts to its metallic form.