Mondreus is the homeworld of the Bounty Hunter Spire, and presumably of the entire Diamont race. As the home of a silicon-based lifeform with a natural ferrous transformation, it's safe to assume that the Mondreus is a telluric planet, primarily composed of silicate rocks or metals, or a combination of both.
- "Spire is the sole remaining member of the Diamonts, an ancient silicon-based lifeform." Metroid Prime Hunters Instruction Booklet, Pg 54
- "Spire's alternative form is the Dialanche, a hypercondensed ferrous orb able to roll at high speeds." —Metroid Prime Hunters Logbook "Dialanche" (Metroid Prime Hunters)