I've made magnesium powder before and frankly its sorta useless, basically explodes when in air. (also this suggestion is basically like wax.)
(Grammar nazi mode) Also the title should be new element*... suggestion***** because you def didnt hack it into the game (although you could've made it in lua but whatever.)
Please refer to this thread before suggesting elements https://powdertoy.co.uk/Discussions/Thread/View.html?Thread=18901
TESC at 0 TMP acts like that, but it is vulnerable to things like BOMB or DEST