Basalt Cobblestone is obtained by mining Basalt from a Volcano. It has a high blast resistance, but is not immune to TNT. When smelted in a Furnace it will become normal Basalt, which can be crafted into Basalt Bricks. It is mainly used for house decorations and structures due to its creeper-resistant properties. It is an easier to obtain alternative to Obsidian. Trying to find a volcano will require you to search far and wide, mostly in a 1000m radius one will be found.