Ancient Stone

Ancient Stone is a new block, generated in the nether, at the same depths as Ancient Debris.  It has the same high blast resistance of Ancient Debris, and it, too, can be moved by pistons.

The brown scaly surfaces which Ancient Debris has on four of it's sides, the Ancient Stone has on all six of it's sides.

When the terrain generator tries to create a blob of Ancient Debris, but aborts because it would be exposed to air, a blob of Ancient Stone is put in it's place.  The terrain generator can replace Ancient Stone with Ancient Debris, but not vice versa.

Post-generation, Two Ancient Stone can be crafted from one Ancient Stone and eight Nether Brick Blocks.

Ancient Stone has slab and stair versions, which can be made in the Stone Cutter.

Although some players might want to build with a new brown block, I suspect it will be more valuable to Restoners as a renewable substitute for Ancient Debris as an unexplodable block which can be moved by pistons.