Black Emerald

The Black Emerald was a large, black coloured Chaos Emerald located somewhere in the southern hemisphere near the Mystic Ruins in the Mysterious Cat Country. It and a group of Chaos Emeralds nearby were worshipped by a group of Chao and protected by the water creature Chaos. After Chaos went rampant and wiped out the Knuckles Clan, the Seven Server Chao absorbed Chaos' energies, transforming into the seven Super Emeralds, while Tikal then imprisoned both herself and the weakened Chaos in the Black Emerald. Hundreds of years later, Dr. Eggman cracked open the Black Emerald, thus releasing Chaos from his captivity along with Tikal. From there, Dr. Eggman unleashed Chaos as his personal water demon, nearly destroying Station Square. After Super Sonic and Knuckles worked together and defeated Perfect Chaos, the water demon and Tikal returned to their imprisonment in the Black Emerald. Additionally, the Super Emeralds transformed back into the Seven Server Chao, who went with Tikal and Chaos into the Black Emerald. (StH: #79, #80, #82, #84, SSS: #13)