Time Stones

The Time Stones (タイムストーン, Taimusutōn) are objects that appear in Sonic the Hedgehog CD. They are seven gemstones that lie dormant on the satellite Little Planet which orbits Earth and have the power to change or manipulate time. In the game, they can be obtained from Special Stages, much like the Chaos Emeralds in most games.

Description
The seven Time Stones are colored red, orange, yellow, green, blue, purple and cyan. When used, they have the power to control time itself and let their wielder move through the passage of time. It is also said they can cause an event of miracles to occur, like transforming polluted water and the surrounding desert into a beautiful lake.

Overview
The origin of Time Stones has not been explicitly stated other than that they are found on Little Planet. The satellite, along with the Time Stones, are able to move through time, which is why Little Planet only appears in Earth's atmosphere for one month every year above Never Lake.

In Sonic the Hedgehog CD, Dr. Eggman attempted to collect the Time Stones in order to take over Little Planet and the rest of the world. Sonic tried to stop his plans by finding them first.

Eggman nabbed one of the Time Stones as he escaped from Little Planet, ultimately causing the events of Sonic the Hedgehog 4.

Trivia

 * Time Stones' similarity to the Chaos Emeralds is striking, in appearance as well as their ability to manipulate time and space. The only major change being that Time Stones are shown to be much larger, as Sonic grabs them after completing a Special Stage.
 * However there seems to be an inconsistency regarding its size, as its shown that Robotnik is holding a single Time Stone in the ending cinematic, which is small enough to hold it in his hand.
 * The major difference between the Time Stones and Chaos Emeralds is that the Time Stones only seem to be able to warp through time on Little Planet itself.