Forestonite is a super energy source found on Earth. Its nature remains largely mysterious.
Generation 2 manga
In August of the year 199X, the Autobots and the Decepticons detected the presence of forestonite on the planet Earth. Decepticon leader Megatron and his Cyberjet warriors Hooligan, Skyjack, and Space Case attacked Japan in search of it, but were repulsed by the Autobots Optimus Prime and Electro. With the Decepticons defeated, Optimus Prime swore to defend the Earth and its forestonite with the aid of the young boy Junpei.
- No, seriously... the manga basically says nothing specific about forestonite. It's on Earth and the Decepticons want it. That's it. We don't even get to see it in action... or even if it's a solid, liquid, or gas. As far as ill-defined super-power-sources go, this is the king.