Basalt pillar

Basalt pillars are tall terrain features made up of basalt.

Info
Basalt pillars are found exclusively in the Nether. They have their starting points in the ceiling of an area, then have a pillar of between one and three blocks wide in both the X and Z axis going all the way down to the ground, where a flat clump of basalt can be found around a 3×3 area from the center of the pillar, as if a vertical lava flow, like those commonly found in the Nether, had solidified.