Petropia is a craggy, geode-like planet where silicon-based beings evolved to build a complex society of separate underground kingdoms.

Universe Ben 10 Universe
Galaxy Milky Way
Class Terrestrial
Atmosphere Breathable
Primary Terrain Crystals
Notable Species PetrosapiensCrystalsapiens

While there are several different gem-based races, from ruby to emerald to sapphire, each with its own distinct abilities and culture, most Petrosapiens now coexist peacefully. After several centuries of warfare, a giant hole was ripped in the sky, revealing a universe far beyond Petropia's heretofore self-contained existence. As its recently enlightened inhabitants have now begun to turn their focus off world, the rest of the galaxy holds their breath, waiting to find out if these crystalline warriors will wage war or come in peace. It was also revealed by Dwayne McDuffie that the planet Petropia is also a part of the Milky Way Galaxy when somebody asked him a question about it.
However, Vilgax has destroyed this planet. But years later it was restored with its people.