Fake Emerald

The fake Emerald is an object that appears in Sonic Adventure 2. It is an Emerald meant to bear similarity to a real Chaos Emerald, but it does not possess the same amount of power, nor can it be used to properly power machines.

Description
The fake Emerald is an exact replica of the Chaos Emerald that Tails was awarded for his deeds in Station Square. Because of this, it is a large, diamond-cut Emerald with a yellow hue, being of the same size and structure that a Chaos Emerald has. Its wavelength and properties are also identical to that of a real Chaos Emerald, meaning that the only way to tell the difference between the two is prior knowledge of which one is real and which is not. Also, one of the major differences between the real Chaos Emeralds is that it becomes explosive when utilized with machinery.

The fake Emerald is less powerful than the real Chaos Emerald, although it seemingly still has chaos energy. Sonic the Hedgehog was capable of using the Emerald to execute Chaos Control, teleporting from a space capsule to the Space Colony ARK from a great distance. This does not appear to be a common occurrence, however, as Shadow remarks that such a feat should be impossible.

History
The fake Emerald was created by Tails sometime after he was awarded a Chaos Emerald by Station Square for defeating the Egg Walker. Using his research on this Emerald, he developed his own artificial Chaos Emerald, one with nearly the exact same properties, but explosive when used in machinery.

Tails eventually brought the fake Emerald onto the Space Colony ARK, developing a plan to place the Emerald into the Eclipse Cannon, destroying it and halting Dr. Eggman's plan to take over the world. Sonic the Hedgehog went off to execute this plan. Meanwhile, Eggman noticed that there was an extra Chaos Emerald signature in the vicinity, and that there must have been a fake. Sonic was about to insert the Emerald into the cannon, when Eggman called him, threatening Amy Rose at gunpoint. Sonic arrived on the scene, figuring that he could easily hand Eggman the fake Emerald, save Amy and destroy the Eclipse Cannon. However, Eggman called his bluff, and trapped the hedgehog in a capsule which he jettisoned into space. Before the capsule could detonate, however, Sonic used Chaos Control with the fake Emerald to teleport back to the ARK in the nick of time.

Figuring he could destroy the Eclipse Cannon by manually inserting the fake Emerald into it, Sonic headed to the weapon. On his way, Shadow the Hedgehog located him, and the two begin a fight where Sonic uses the fake Emerald to do Chaos Control. After the fight, Sonic inserted the fake Emerald into the Eclipse Cannon, destroying the latter.

Sonic X
In Sonic X, the fake Emerald was created by Tails in the Season 2 adaptation of Sonic Adventure 2. It essentially serves the same purpose that it had in the game.

In Season 3, the Metarex initiated a plan by the name of Operation Duplicate, in order to distract Sonic and his friends to prevent them from gathering all the real Chaos Emeralds.

Hundreds of these Emeralds were mass produced, with similar abilities, but lesser power than the normal Chaos Emerald. They were incredibly brittle and could easily be crushed or burn out after a single use. These Emeralds were capable of inducing Chaos Control and could also initiate a Super transformation in the form of Dark Sonic. After Dark Sonic’s usage of the fake Emeralds, they were all completely rendered useless.

Trivia

 * In many older Sonic games, such as Sonic the Fighters and Sonic the Hedgehog Spinball, the number of Chaos Emeralds fluctuates. Many fans have attributed this to one or more fake Emeralds.
 * When Team Dark uses their Team Blast, Chaos Inferno, there is a Chaos Emerald that is used to induce the move. Many fans have presumed that Emerald was a fake, but canonically, it likely was the green Emerald that Team Dark produced in the cutscene before the battle against Metal Sonic.