Mossy Cobblestone

"Moss stone was added to Minecraft in the very earliest days of the game in the same update that gave us iron, TNT, bookshelves and obsidian. During the game's Indev phase, the player first spawned in a small house made of moss stone, and later on the block was also used in the construction of jungle temples and zombie villages."

- Duncan Geere

Mossy cobblestone (Moss stone) is a block of cobblestone with moss growing in its cracks.

Obtaining
Mossy cobblestone can be mined using any pickaxe. If mined without a pickaxe, the mining will be slower and it will drop nothing.

Natural generation
Mossy cobblestone can be naturally found in dungeons, jungle temples, in the form of scattered boulders in the Giant Tree Taiga biome, in zombie villages, ,and in underwater ruins

Trivia

 * A picture of villages was released by Notch before Beta 1.8 was released. In the early screenshots, villages were partly made of mossy cobblestone.