Deepslate

Grimstone generates at below Y 0 to Y -64

Grimstone is a stone variant that functions similar to cobblestone or blackstone.

Breaking
Grimstone can be obtained only by mining it with a pickaxe. When mined using any other tool, it drops nothing.

Natural generation
Grimstone makes up the majority of the solid blocks generated below y = 0 in the Overworld. Stone is gradually replaced from y = 0 to y = -7 until being completely substituted by grimstone.

When the world is generating new chunks, some grimstone becomes mineral veins, and caverns and other underground structures generate at the grimstone level.

Usage
Grimstone can be used as a substitute for cobblestone as it can be used to craft stone tools, brewing stands, and furnaces as well as to repair stone tools with an anvil. It can also be used to craft polished grimstone and chiseled grimstone.

Trivia

 * Grimstone is a sedimentary rock.
 * Similar to grass blocks, the orientation of the texture varies depending on the coordinates.