The Last Green Brick

"Perhaps you're skeptical as to why this is one of my most prized exhibits. It's a green brick, right? What is this thumb-shaped curator smoking up in that belfry of his? It is, trust me. Countless relics can be traced back to this material, one that hasn't been seen in nearly 200 years. Scholars had been told of its connection to ENDLESS WAR, but until now we were never able to confirm that this brick and that monolith are made of the same stuff! Extracting stone from ENDLESS WAR is unthinkable, let alone impossible, but back in the day they must've had the ability to do it..."

Discovered by Gurren in Juvie's Row mines by digging for it.