Fireworks!
One of the things I enjoyed back then, I would usually ask Will to take me to such events as they brought me a bit of excitement, of course, I had no one to watch them with other than the poker faced butler, but it was still better than nothing…
To explain it simply, the reaction of the two elemental crystals just now was due to the crystal's incapability of housing both corrupted and pure elements that were trapped inside, and without being able to release one of them due to the 'Elemental severing' barrier, the crystal decided to commit suicide relying on the power of my lightning and thunder elements.
If one was to somehow force two similar poles of magnets to touch each other, they would normally explode away as soon as the power forcing them to be stuck together vanished.