Fire

Fire is a block that was first seen in Indev. It has an animated face on all four sides, and two faces on the inside at slants. Fire is not created naturally in a map, it will only be created if the player causes it.

Fire is only available for use in Indev and Infdev. It cannot be directly placed (although it could be in an old Indev version designed to test out fire), but rather by using Flint and Steel. When placed, the fire will burn for a short time. If nothing flammable is next to it, it will die. Planks, Trunk, Leaves, Cloth and Bookcase blocks are all flammable. Fire will also cause TNT to detonate. Fire will spread over flammable surfaces, slowly causing all the blocks it can reach to burn away. Fire can climb up walls, across floors and ceilings and over small gaps.

As one would expect, any mob (including the player) will be lit on fire if exposed to it. The fire will obstruct the player's view slightly and they will slowly lose life. The fire will burn out after a while, but it is a good idea to try and jump into some Water as soon as possible. Fire can be used as an attack against mobs. Lighting fire to dropped items or blocks will cause them to burn away. This trick can be used to dispose of materials quickly. Anything that touches Lava, mob or dropped object, will be lit on fire.

Chainmail Armor
Due to a bug, it is possible to craft Chainmail armor out of fire blocks. It is only possible to get actual fire blocks in the players inventory by means of hacking it.

See this video.