An explosion that does not damage blocks. Instead, it randomly transmutes any material in the blast radius to anything that is equivalent to it. Perhaps even merging a few objects here and there into higher valued items, or breaking some into lower valued items (equivalently).

I haven't quite thought of occasions when this might happen, as i don't know to much about the current mechanics of EE3. Perhaps something to do with putting something bad in red water or trying to transmute something you can't? Maybe even a dying stone.

trying to transmute something you can't?
So alchemical energy will reflect from not transmutable block(like bedrock) and will transmute everything in radius? I like it.

Yeah, stuff like that. Maybe even an alchemically explosive block like TNT, just transmuting instead of destroying.