Gem

Gems are small crystals introduced in Sonic the Hedgehog (2006). They are the upgrades that Sonic can use to alter the appearance and colors on his shoes to gain special abilities.

When beginning as Sonic, you'll talk to an old man named Alberto Robert, a shoemaker who claims to have made the ultimate shoes that use the power of Soleanna's mysterious stones to change. He gives Sonic a pair of Custom Shoes to try out and, after the first Town Mission of the game, is so proud of them he lets Sonic keep them. He also states that they react to the local gems of Soleanna, which can be bought at the shop.

The abilities are selected using the D-Pad, and activated by holding or pressing R1/Right Trigger.

Trivia

 * The gems are "emerald cut", and thus look like the Sol Emeralds.
 * In the demo, there has been hinted that an eighth Rainbow Gem would have been included but the idea has been scrapped as the gem's function hasn't been completed. However it is believed to cause Sonic to become Super Sonic.
 * Due to the rushed nature of the game, the gems not only are incredibly buggy, broken, or useless to use, the bar that was included to limit their usage was not implemented correctly, allowing infinite use of the abilities.