Urthic Ore

From Wikitroid, the Metroid wiki

Urthic Ore composes most of Zebes's crust and was briefly mentioned in Metroid Prime. It is considered "ideal for subterranean construction." The official website states that Bendezium is "commonly found on planets with crusts containing 85% or more Urthic ore."

The name shares a close etymology with the Urtragian Shriekbat, though the connection, if any, is unclear. By association to the creature, it is possible that the material found on the Pirate Homeworld's mining facility is Urthic Ore. The Pirates had large drills and were possibly mining the substance.

[edit] Metroid Manual

"The planet Zebes is a natural fortress. Its sides are covered with a special kind of stone, and its interior is a complicated maze."