Elemental Plane of Earth
From Ardrana
Press against a solid stone wall - that's what the plane of Earth is like. Solid and unyielding, this plane is one of the Inner Planes that's least open to travelers. A cutter can't fly through it like the Elemental Plane of Air, swim through it like the Elemental Plane of Water, or sail on it like the Elemental Plane of Fire. It's a universe of unbreached rock.
Still, there's reasons for going there. Armorers and swordsmiths will pay a fine price for iron dredged from the heart of the plane, and jewelers cherish the stones pried from it. But there's a lot of danger on it, too. A being can get lost without even trying, as there's no landmarks or clear expanses to guide him on his way. Plus, wander away from the heart of the plane and Earth becomes Dust, Magma, or Ooze - all almost as difficult and just as deadly.
The plane of Earth is separated from the Elemental Plane of Fire by the Paraelemental Plane of Magma, and from the Elemental Plane of Water by the Paraelemental Plane of Ooze. Where the plane of Earth meets the Positive Energy Plane is the Quasielemental Plane of Mineral, and where it meets the Negative Energy Plane is the Quasielemental Plane of Dust.
Note: The Elemental Plane of Earth originally appeared in the Planescape AD&D campaign setting from TSR. Its use here is for the purposes of providing context for the campaign only.