Netherrack

Netherrack (formerly known as Netherstone ) is a rock-like block found in the Nether.

Obtaining
Netherrack can only be collected with a pickaxe.

Natural generation
Netherrack makes up most of the Nether's terrain.

Usage
When netherrack's top is lit on fire, it burns infinitely.

Trivia

 * Netherrack can be mined in 0.05 seconds with a golden pickaxe (or a diamond pickaxe enchanted with any level of efficiency). However, there is a .25 second delay between mining blocks. It can be instantly destroyed by an efficiency II diamond pickaxe or better, and there is no .25 second delay, because the time needed to mine it is less than one game tick.
 * In the game code, it is referenced as "hellrock".