The master emerald

Excerpt:
The Master Emerald is a GIGANTIC glimmering green jewel that has almost unlimited magical power, as far as anyone knows. It is a Chaos Emerald, though it is the only one of its kind--the only one that large, or that strong, again, as far as anyone knows. It calls the other Chaos Emeralds to it and sort of links them together--well, the Super Emeralds, anyway. And it might be special in...OTHER ways...too...
It was found underneath the city of the Echidna-people when they were first building their civilisation, and once they found out what it was and what it could do it became one of...