Mossy Cobblestone

Mossy Cobblestone is almost the same as normal Cobblestone, the only  difference being that it is covered in moss. It is often used in combination with normal cobblestone to make buildings look old and like  ruins. In Alpha mode, it is currently only found in underground Dungeons, though it can be mined and used like normal  Cobblestone. However, unlike standard Cobblestone, it cannot be smelted into anything at this time.

Notch has stated that moss will grow on normal cobblestone in the future, and there is  speculation that it will spread to other cobblestone blocks as well,  making it similar to how Grass grows on Dirt. This is a low priority task, however.

Mossy Cobblestone looks very similar to Netherstone in that both blocks are similarly textured, with Mossy Cobblestone being grey with green moss and Netherstone being  bright-red with dark-red moss.

Bemooster Pflasterstein