Pure pieces of mana.
When Tyra Kolaq’blegae was first created there was one solar system revolving around a sun of pure mana, the first instance of mana. It gave life and took it away. Eventually for an unknown reasons it shattered, it burst. It pulled all of the planets in, and then ruptured, sending them out across Tyra Kolaq’blegae. Mana spread across the universe, unevenly. Most of it was tiny particles. But some were more whole.
Mana Shards are the pieces of that explosion, part of the first sun. They radiate mana. They are the seeds of Mana Trees.