Chaos emeralds

The Chaos Emeralds are seven fictional emeralds from the Sonic the Hedgehog video games. The Chaos Emeralds have mystical properties and abilities, and the holder of them all can use them for a large variety of things, such as transforming into a powerful "super form" and teleportation. Each emerald is composed of positive and negative charged materials which make them an everlasting source of energy and allow them to float in the air. All player characters that are capable of transforming only use the positive charged part of the Emeralds to do so, which is demonstrated by Sonic at the end of Sonic Adventure (except possibly Shadow, who has been shown using positive and negative energy in Shadow the Hedgehog and Sonic Adventure 2 respectively). Sonic the Hedgehog is the only character seen with the ability to merge with the chaos emeralds when transforming into Super Sonic, shown in Sonic Unleashed and Super Smash Bros Brawl. After a super form is reached, the Emeralds discharge and send themselves across the world (or to Special Stages), and as such characters often collect them throughout the games. While they were more like "bonus" items in the early games of the series, the Chaos Emeralds became necessary plot devices in Sonic Adventure, and that trend has continued throughout the later 3D games.

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The Chaos Emeralds' backstory are shrouded in mystery, and they are known to have existed for thousands of years, along with the larger Master Emerald. The games and comics have revealed that both the Echidna and Babylon civilizations that existed thousands of years prior to the games knew about the Chaos Emeralds, along with the Black Arms, who have visited Earth for at least 2000 years. The civilization that created Emerl over 4000 years prior to the games is also known to have been experimenting with the Chaos Emeralds. The Chaos Emeralds were named such by the remaining Echidnas due to their connection with Chaos, who destroyed their civilization.

According to Sonic Adventure, the ancient saying associated with the Chaos Emeralds and the larger Master Emerald is "The servers are the seven Chaos. Chaos is power. Power is enriched by the heart. The controller is the one that unifies the Chaos." The meaning of this saying is further clarified in Sonic Adventure 2 by the Master Emerald's power to neutralize the Chaos Emeralds, and in Sonic the Hedgehog where their ability is described as being able to "transform thoughts into power."

While the Chaos Emeralds can lie around basically anywhere, they can quite often be found in Special Stages (also known as "The Special Zone"), strange alternate dimensions. Even alone, their power is unmatched by anything else in the universe; except perhaps by the Master Emerald, which is just as powerful as all seven Chaos Emeralds, if not more.

The Chaos Emeralds in themselves are usually used for weapons of mass destruction (in Doctor Eggman's case), Chaos Powers (normally the case with Shadow the Hedgehog), and letting people turn into their Super forms (pretty much everyone). The energy can also be given from one super form to another character to allow that person to achieve a super form of his own (for example, at the end of Sonic Heroes).

It is not known why the Chaos Emeralds need collecting at the beginning of every game (except, of course, for the purpose of game dynamics). One explanation is that after the Chaos Emeralds are used to their maximum strength, they repel each other and so end up in Special Stages (early games) or just the "four corners of the world" (later games), very much like the Dragon Balls from the Dragon Ball franchise.

However, there is one exception to this explanation. During the opening sequence for Sonic the Hedgehog 3 (if you chose Sonic or Sonic & Tails as your character choice), Sonic is in possession of all seven of the Chaos Emeralds at the beginning. This is evident when he leaps off the Tornado and falls off-screen only to come racing across the ocean as Super Sonic before making his way onto Angel Island. There, Knuckles then steals the Chaos Emeralds and hides them from Sonic so that he has to search from scratch like all other games. Thus, another explanation could possibly be that Sonic himself hides them so their power won't fall into the wrong hands, and so all of them won't be in one group for "easy picking".

Because of the huge power emanating from each emerald, creating radars to track them are relatively simple (Rouge, Tails and Eggman all had one in Sonic Adventure 2, and Tails used one again in Sonic Riders). Each emerald is linked to each other, and as Tails describes, act like magnets attracting each other, allowing him to discover Eggman's location on the ARK. Knuckles and Shadow also seem to have the natural ability to sense an Emerald's power.

Many fans believe that Sonic and co. have lost the emeralds after each game, but once Sonic or anybody else uses their super form, once their super form ends the emeralds scatter.