Minecraft wiki entry for Deepslate, associated text: According to Brandon Pearce, the reason for changing the name "grimstone" to "deepslate" was because the word "grim" had too many connotations related to a negative feeling and therefore did not accurately describe the block as to what it actually was. The name "deepslate" was eventually chosen because of its location within the world and to more accurately represent that it is a type of slate.[2]
Similar to stone, the orientation of the texture varies depending on the coordinates.