Minecraft/Cobblestone

Very common, cobblestone is the next stage up after wood, being more durable and impervious to flame. Cobblestone is great to build with in the early game, as it offers relatively high durability compared to wood or dirt with only a little effort. This also frees up wood to be used more exclusively for crafting or decoration. Shortly after the player begins mining in earnest, they will quickly begin to accumulate cobblestone, and will often find themselves with much more than is immediately needed. Even later in the game, cobblestone is often used for temporary structures, or for very large external structures where some durability is desired (For example roadways).

Obtaining
Cobblestone make up dungeons, jungle temples, and outposts to name a few and is dropped by stone.

You can also get it when flowing water touches flowing lava.

Crafting
Cobblestone is used in a lot of recipes such as dispensers, droppers, furnaces, and levers (etc.).