Sonic Rush Adventure
Sonic Rush Adventure marks the first appearance of treasure chests, where they are found at the end of each Act (except bosses). In this game, they are light brown (with a touch of yellow flames) with yellow and purple edges and a small red jewel at the tip. Instead of a lock, they closes with a tether.
Treasure chests can be opened by attacking them. They will then rotate briefly before opening, upon where they show a sparkling aura before moving onto the results screen. In normal Acts, treasure chests contain different Materials. During Marine's fourteen search missions however, they contain Medals instead.
Sonic and the Black Knight
In Sonic and the Black Knight, treasure chests can be found during the game's Missions in Adventure Mode. In this game, they each contain a collectable item, some of which can be exclusively found in them. To open a treasure chest and obtain the item inside, the player simply has to touch it. Like all other items, the item gotten from the treasure chest does not have an immediate effect, and must be identified at the Item Identification screen.
A type of the Knights of the Underworld resembling treasure chests also occasionally during Missions. They usually grant an amount of Rings when attacked or touched, though they can hard to make contact with due to their movements.
In the Nintendo 3DS version of Sonic Generations, the treasure chest is the counterpart to the Collection Room; from it, the player can select events, music, concept art, and models (which are unlocked automatically by clearing missions). The treasure chest's design is very similar to those ones from Sonic Rush Adventure.