Soul Soil

Soul soil is a block naturally found only in the soul sand valley.

Natural generation
Soul soil generates naturally in the soul sand valley biome.

Obtaining
Soil soil drops as an item when broken with any tool or by hand, but a shovel is the fastest way to break it.

Fire
Fire lit on soul soil becomes soul fire.

Withers
4 blocks of soul soil (or soul sand) are used in the construction of a wither.

Trivia

 * Unlike soul sand, soul soil does not slow mobs down.