Petropia is a craggy, geode-like planet, and the homeworld of the Petrosapiens.
Petrosapiens built a complex society of underground kingdoms.
After several centuries of intra-planetary warfare, a giant hole was ripped in the sky, revealing a universe far beyond Petropia's heretofore self-contained existence.
Prior to The Secret of Chromastone, Tetrax, while exploring the ruins of the planet, learned what the true nature of the crystal was. He then stole it back from Vilgax and gave it to Sugilite. It was used to restore Petropia and its people by Ben (as Diamondhead). The crystal was returned to its home and given to its guardian, Sugilite, when he was revived, where it will be protected. Petropia is guarded by Sugilite.
- Ben 10: Secret of the Omnitrix (flashback)