Chaos Emeralds

A Chaos Emerald is a mystic item that appears in the Sonic the Hedgehog video games, allowing the holder of all seven of them to transform into a "super" form. Each emerald is composed of positively and negatively charged materials which make them an everlasting source of energy and allow them to float. This energy also makes their possessors faster than normal.

Sonic and Knuckles only use the positive charged part of the emerald to transform, which is demonstrated by Sonic at the end of Sonic Adventure. Knuckles has only been able to transform in Sonic & Knuckles and Sonic 3 & Knuckles. Tails was also able to attain a super form with the use of both the Chaos Emeralds and the Super Emeralds in Sonic 3 & Knuckles.

The Chaos Emeralds can be anywhere, usually located in a "Special Stage". Even alone, their power is unmatched by anything else in the universe; however, their power can be halted at any time by the Master Emerald.

With the exception of Sonic Heroes, nearly every mainstream Sonic Game has revealed something new about the Emeralds — it could be almost taken that the series is somewhat centered around them.

Introduced in Sonic the Hedgehog, there were 6 Chaos Emeralds located in 2D rotating Special Stages, and Sonic could not become super. Sonic 2 was the first game to introduce all 7, in pseudo-3D Special Stages in which Sonic and Tails continuously run forward down a half pipe. Sonic 3 revealed where the Emeralds really come from and Sonic & Knuckles revealed the Master Emerald. In both, the 7 emeralds are located in pseudo-3D special stages that rotate entirely when you turn. You must collect all the Blue Spheres located in the stage to earn the Emerald. The first two GG/SMS games had emeralds located inside the actual levels. From Sonic Chaos and beyond, the emeralds would be found in special stages like in the 16-bit games.

The Chaos Emeralds appear as plot points in Sonic Adventure and Sonic Adventure 2. In Sonic Adventure, the Chaos Emeralds were collected by Dr. Eggman in order to feed Chaos, a water beast that changed form every time it received a Chaos Emerald. With all 7 it became Perfect Chaos, and used all of the negative energy in the emeralds before dropping them onto the ground. Sonic then picked all 7 up and used the positive energy to become Super Sonic and defeat Perfect Chaos.

In Sonic Adventure 2, Sonic and Shadow had the ability to use the Chaos Emeralds to perofrm "Chaos Control": alter time and space to teleport or freeze time. Shadow collected the Emeralds for Dr. Eggman to power the ARK, at which point Biolizard took over the station. It became FinalHazard, and then Sonic and Shadow had to team up and use the Chaos Emeralds (it is believed Sonic used the positive energy and Shadow used the negative, but no proof has been given) to become Super and defeat FinalHazard.

Sonic Heroes, being more of a deviant game like Sonic CD or Knuckles' Chaotix, revealed nothing new.