Ebonstone Block

Ebonstone is a rock that can only be destroyed with higher tier pickaxes (Nightmare Pickaxe and Molten Pickaxe) or Dynamite. Chasms are comprised of these blocks.

You can turn it into normal stone with Purification Powder.

Placing Ebonstone will spawn the Eater of Souls, and the Devourer when placed near or below ground level; as such it is usually not a recommended building material. Building a house out of Ebonstone is certainly not advisable. It can be useful for farming Rotten Chunks when placed well above ground and confined with other block types and a Door, as Eater of Souls will spawn in the confined space and be relatively easy to kill.

As of patch 1.0.5, Deathweed can grow randomly on Ebonstone blocks.