Acwastone is a liquid mineral that keeps its shape. It is made from the Blue Light, and forms the centre of the Jewel of Dagda.
The Jewel of Dagda used to belong to one of the Ossada, who transferred some of his power into it as a way of keeping himself alive.
The Jewel Of Dagda
Dagda was a very powerful warrior, and one of the Ossada. As such, he could use the Red Light very well. To help keep himself alive, he moved some of his power into his jewel (The Jewel of Dagda) so that, if he was wounded in battle, the jewel would be able to heal him instantly. He died eventually when he grew tired of the world and removed the jewel from his wrist.
The Jewel then faded into myth and was kept with other relics of the Ossada in Llyn Dinas.
None of the Guardians have the same amount of power that is concealed within the Jewel. If worn, the acwastone will give power to the wearer over a few weeks. If it gave the infinite power straight away, the sudden change would kill them.
After a few weeks, the wearer gains the Red Light through the jewel, making them one of the most powerful beings on the Earth.
To a human, the jewel is just a jewel and would do nothing more than giving them a heightened sense of right and wrong.