- For the jewel in Sonic Underground, see Power Stone. For the pair of stones in the Sonic the Hedgehog television series, see Deep Power Stone.
Power Gems, also called Power Stones, are energized minerals 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. Supposedly, it is one of the rarest occurring natural elements, second only to the Chaos Emeralds.
Due to an unknown fluke, a Power Gem 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)
Years later, Dr. Ivo Robotnik used a Power Gem to boost the power of the original Metal Sonic, which caused him to transform into Titan Metal Sonic v2.0. However, Knuckles also used the gem's power to enlarge himself, and defeated the robot. Despite this, Metal Sonic survived and after being convinced to surpass his programming, his Power Gem survived being buried in lava and repaired him. He later located and fought Sonic, defeating him with ease due to having the Power Gem embedded in his chest. However, Metal Sonic sacrificed his life to save both Sonic and Tails on Mount Mobius. Metal Sonic's Power Gem was eventually recovered by the Royal Secret Service, but was captured by Dr. Eggman upon his uprising. Geoffrey St. John managed to steal Metal Sonic's Power Gem back and gave it to Sir Charles Hedgehog, who used it to help create the Metal Sonic Troopers and later build it into Metal Sonic when he was rebuilt as Shard, providing him with a steady source of power while also helping with self-repair.
Dr. Eggman retained one Power Gem from his predecessor's supply and decided to use it to improve his Metal Sonic v3.7 model by imprinting it with the combat data from all the previous Metal Sonic incarnations for Metal Sonic v3.7 to access. With the information granted by the Power Gem, Metal Sonic v3.7 engaged Shard in battle and managed to gain the upper hand, 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.
- The Power Gems appear to be similar to the Power Crystals from the early Crash Bandicoot games, albeit green as opposed to purple.