Control crystal

Control crystals are power sources from the Generation 1 continuity family.

This caption points out the obvious, as does Grimlock.

Control crystals are good for about everything. They can power spaceships, cure or prevent (organic) illness, store minds and grant Transformers near invincible strength. And that's just the known list of of uses. So of course, they are ridiculously hard to come by.

Fiction

The Transformers cartoon

The Heart of Cybertron would seem to be a control crystal. Microbots

Marvel UK Comics continuity

The shuttle that brought the Dinobots to the Savage Land contained a control crystal, which was left behind when the Dinobots engaged Shockwave in battle and got buried alive with him. Millions of years later, a human named Professor Embrey found the ship and took some of its parts, including the control crystal, to build himself a home for the duration of his stay in the Savage Land. Moreso, when a strange disease hit the native dinosaurs, he found that the control crystal's radiance kept the disease away. Knowing this, he enclosed an amount of land around his hideout to keep a number of dinosaurs near and thus save their lives.

In 1992, Snarl's case of Corrodia Gravis had gotten to an advanced stage and still there was no cure. The only thing the Dinobots could think of to save their teammate was to get a control crystal and store Snarl's brainwaves in it while they'd get him a new body. The sole control crystal they knew to still exist was the one from their old shuttle, so they went to get it. Finding the crystal missing, they searched the Savage Land, homing in on the control crystal's energy aura and encountering many sick or dead dinosaurs on the way. Upon finding the control crystal, Professor Embrey begged the Dinobots not to take it away from him and his healthy dinosaurs. Swoop suggested that they could use the crystal to transfer Snarl's mind into a stegosaur and that Embrey would look after him in return for keeping the crystal. That suggestion was agreed to by all parties (except maybe the stegosaur). Destiny of the Dinobots!