u/GaIarianSlowking

Mega Evolution and Terastallization are connected. As far as I know, Mega Stones are formed when a Pokémon dies to an extreme ammounts of energy. My idea is that the Tera Shards inside a Tera Orb are incomplete Mega Stones. They aren’t strong enough to Mega Evolve a Pokémon, but they can still alter a Pokémon’s type, similar to how some Mega Evolutions change the Pokémon's type.

This idea is supported by the fact that Mega Stones were created from the energy released by the Ultimate Weapon when it fired. Assuming that blast made the Crator of Paldea, then Tera Shards could be a byproduct of that fallout.

I would love to hear your thoughts.