Chaos Emeralds

Chaos Emeralds are a recurring feature in Sonic the Hedgehog series.

Overview
In the games, Sonic had to collect all 7 (6 in the first game) Chaos Emeralds in order for him to turn into Super Sonic. In the older games, the Chaos Emeralds were hidden in Special Stages. In the recent Sonic games (more specifically, the 3D games), Chaos Emeralds were required to progress through the games.