The Chaos Emeralds are gems collected in the Sonic the Hedgehog series. Their first appearance was in the original Sonic the Hedgehog, where there were only six. In subsequent games, the amount was increased to seven and has remained at seven, with the exception of Sonic the Fighters. It should be noted that though there are technically only seven emeralds in Sonic the Hedgehog 3, an eighth emerald was able to be obtained through a glitch or a code.
The Chaos Emeralds have been around for thousands of years and are the source of tremendous power. Throughout the Sonic games they can be seen being used to power several machines, such as Dr. Eggman's robots and the ARK's Eclipse Cannon. They also have the ability to transform the player into a " Super Form". To transform, the player needs to have collected all the Chaos Emeralds, have 50 rings, and then hit the jump button in mid-air. Once transformed the character is given invincibility, flight, super speed, and the ability to damage enemies simply by contact. This form will not last forever though as the ability to maintain this form is based on the player's constantly decreasing supply of rings. Sonic, Knuckles, and Tails each have their own unique ability in the 2D games. In his Super Form, Sonic will release a flash of light that damages all the foes on-screen. Knuckles will release energy whenever he climbs on a wall, and Tails gains three birds that will follow him around and attack his enemies. In the 2D Sonic games the emeralds were obtained through various special stages, but in the 3D incarnations acquisition of the emeralds is more closely tied into the actual plot. The emeralds' power could also be used to access an power called "Chaos Control" that allows the the user to control space and time giving him the ability to teleport.
Super Emeralds and The Master Emerald
The Super Emeralds first make their appearance in the game Sonic 3 & Knuckles. These are essentially the 7 Chaos Emeralds that have been powered up by the Master Emerald and allow further transformations in the old 2D games. They allow Sonic to go beyond Super Sonic and become Hyper Sonic. This is also true of Knuckles. However Unlike the other two characters Tails does not get a transformation from the original 7 Chaos Emeralds and needs the Super Emeralds in order to gain his transformation in the game. The Super Emeralds are kept on the Floating Island, Knuckles' home, and sit along side the Master Emerald in the Hidden Palace Zone. After deceiving Knuckles to fight Sonic, Robotnik steals the Master Emerald which causes the floating island to fall to Mobius.