This page is about Chaos Emeralds enhanced by the Overmind. You may be looking for the Super Emeralds.
Great Emeralds (グレートエメラルド,Gurēto Emerarudo?) are Chaos Emeralds that were psychically treated by the Voxai leaders, the Overmind. They display a pinkish hue from the process.
After Imperator Ix took the Chaos Emeralds and the Master Emerald from Sonic's world, he placed a Chaos Emerald in each colony. For some reason, he placed two Emeralds on Voxai Colony Beta and Voxai Colony Alpha. After the Overmind obtained the two Emeralds, they treated the Emeralds and changed them into Great Emeralds. But the Overmind then became mad with power. Originally, they were kind and asked their people to accomplish great things, but when they Chaos Emeralds came, they "no longer asked, they demanded." Sonic and his friends came to Voxai Colony Beta, one of the local residents, Thebes, told them about the Overmind and Great Emeralds. They tried to reach a portal that would take them to Colony Alpha, but one of the Overmind's elite guards, Thelxe cut them off and fought Sonic and lost. After losing, Thebes took a Great Emerald from Thelxe, as well as a mental passcode, and gave them to Sonic. Thebes then stayed behind on Colony Beta to "keep his mind on him [Thelxe]." Sonic and his group then travel to Colony Alpha to fight the Overmind. The group ended up being possesed but Sonic was immune to their mind control. Overconfident, the Overmind gave Sonic his friends back, which proved to be their downfall. After the fight, the Overmind lost and Sonic got the Great Emerald and Thebes decided to takeover as Overmind. At some point, the two Great Emeralds changed back into Chaos Emeralds.