Cobblestone

Cobblestone is a common block used for creating various items, that resembles an uneven, roughly paved surface. Cobblestone only occurs naturally in dungeons, NPC Villages, strongholds, or when water and flowing lava come into contact. It is commonly used to create walls for constructions with a medieval appearance such as castles, towers and roads. Cobblestone is obtained by mining stone. Cobblestone is slightly harder to mine than normal stone, and there is an alternative version of the block known as Moss Stone, which can only be obtained from dungeons. Silverfish have the ability to enter and hide in cobblestone.

Uses
Cobblestone is a basic building block required for the crafting of many essential tools and items.

Cobblestone is required to craft furnaces, Cobblestone Slabs, stone stairs, stone tools and weapons, levers, Pistons, dispensers and Brewing Stands. Because of its fair blast resistance, immunity to Enderman griefing, and the abundance of stone, cobblestone is a very commonly-used building material(although viewed by some as ugly). Cobblestone can be smelted back into smooth stone in a furnace.

Stone tools are easy to craft and widely available early in the game, making them very efficient even when iron is accessible. However, they possess the lowest enchantability of all tool sets, surpassed even by wooden tools.

Trivia

 * Cobblestone is created when water attempts to flow into a block already occupied by flowing lava.
 * This means that infinite amounts of cobblestone can be created by a generator, technically qualifying it as a renewable resource.
 * When water flows into the source block of lava, it creates obsidian instead.
 * Cobblestone is resistant to Ghast fireballs, making it useful for guarding portals.
 * Until the release of Beta 1.3 cobblestone was used to create stone slabs.
 * Cobblestone makes up the walls and, along with Moss Stone, the floor in dungeons.
 * In the game's source code, Cobblestone is referenced as "stonebrick."
 * The current texture for cobblestone has the top and bottom halves swapped and brightened.
 * Although cobblestone is clearly riddled with faults and cracks, it has a higher blast resistance than most blocks and is on par with many others (including stone).
 * You can find naturally occurring cobblestone in dungeons, NPC villages, or places where lava and water flow together.
 * In the 1.2.5 pre-release, looking at Smooth Stone in creative mode and pressing the "Pick Block" button will give you/select Cobblestone.