This is coal. Tis' another material that is vital in this game. You CANNOT make tools with this material. But, you can make some torches as shown below. Coal was added in classic v0.0.14a and has been updated 3 times since then. In Classic v0.0.28 it was obtainable from the creative menu. In indev v0.31 it was made so if broke by hand it gave 1 coal and if mined with a pick it gave 3. And in full release 1.3.1 it gives xp if mined (Like the other ores). In 1.5.2 It was made possible to make coal blocks which I believe you can use as a longer source of fuel.