Power Gems (also called Power Stones) are an energized mineral similar to Chaos Emeralds found on Mobius. Properties of Power Gems include increased all around power, the ability to increase the size of objects, and the ability to upgrade or power machines. Unlike Chaos Emeralds, however, Power Gems were produced artificially by Dr. Ivo Robotnik.
At some point in his efforts to take over Mobius, Dr. Robotnik created Power Gems to serve as energy sources for his weaponry and technology. Due to an unknown fluke, one temporarily transported Sonic the Hedgehog, Mighty the Armadillo and Ray the Flying Squirrel into an alternate zone; it apparently affected the flow of time as Sonic and Mighty reappeared almost instantly despite having experienced a longer time within the zone itself, and Ray, who was later found trapped with the gem, experienced what seemed like mere hours to him over the course of nearly a decade. (KtE: #26, #27, #28, KCX)
Years later, Robotnik used a Power Gem to boost the power of his Metal Sonic v2.0, which caused him to transform into Titan Metal Sonic v2.0. However, Knuckles used the power of a second gem to enlarge himself, and defeated the robot, while the other gems were stolen from Robotnik by renegade robots Heavy and Bomb. Despite this, Metal Sonic survived and repaired himself. He later located and fought Sonic, defeating him with ease due to having the power gem embedded in his chest. Metal Sonic sacrificed his life to save both Sonic and Tails after being convinced to surpass his programming, though his power gem survived the lava flow from Mount Mobius and was later incorporated in the robot once he was rebuilt as Shard, providing a steady source of power while also helping with self-repair. (StH: #86, #87, #238, KCX, SU: #41)
Dr. Eggman retained one Power Gem from his predecessor's supply, and decided to use it to improve his latest Metal Sonic v3.0 model. Imprinted with combat data from all the previous incarnations, Metal Sonic v3.7 engaged Shard in battle, but eventually realized that the Power Gem was a weakness as well as an advantage. As such, it caused the gem to self-destruct, cracking Shard's gem core in the process. Metal Sonic was subsequently rebuilt into version 3.8, retaining all the abilities of its predecessor despite the loss of the gem. Metal Sonic reported the destruction of both Power Gems, but Shard's fate following the encounter was never learned. (SU: #50)
- The Power Gems were an artistic liberty taken with the adaptation of Knuckles' Chaotix; they were not featured in the actual game.
- The Power Gems share some similarities with the Deep Power Stones from the animated series.