Gem

Gems are small crystals introduced in Sonic Next-Gen. They are the upgrades that Sonic can use on his shoes to gain special abilities.

When beggining as Sonic, you'll talk to an old man named Robert who makes shoes. He gives Sonic a pair of Power Sneakers to try out and after the first Town Mission of the game is so proud of them he lets you keep them. He also states that they react to the local gems of Solleanna which can be brought at the shop

Trivia

 * The Gems look like the Sol Emeralds and perhaps based after them, though the size of these gems are never stated other than that Robert states that Sonic's footwear react to them. Pressumably small to fit into the shoe.
 * In the demo, there has been hinted that an eight Rainbow Gem would of been included but the idea has been scrapped as the gems function hasn't been completed. However it is believed to cause Sonic to become Super Sonic.