Diorite Cobblestone is a block added by Better With Mods. Similar to vanilla Cobblestone, Diorite Cobblestone is dropped when breaking Diorite. The block was added for consistency with vanilla Minecraft's stone. Diorite Cobblestone can be used in place of cobblestone in many recipes.
Diorite Cobblestone, along with other Cobblestone drops from the mod, can be turned off in the config file under the HCCobblestone option.