Lava

Lava is a fluid block. Sources of flowing lava can be found in subterranean caves, and occasionally at the surface. Still lava can only be found deep underground, near the bedrock layer. Contact with lava is dangerous and deals damage to players and mobs.

Management


In Classic, lava spreads by duplicating itself to open horizontal and downwards squares like Water. Lava is slower, though, and can be easily outrun. A quick player can block the flow of lava by building a dam. However, if the lava wave is large, a player may not be able to build fast enough. Also like water, lava slows down the player moving through it but it does so to a greater extent. Lava is also more opaque than water and is harder to see through while you are submerged. You cannot see through lava from outside it.

If a horizontal lava flow collides with water, Cobblestone is created, but if a vertical lava flow collides with water, the water is removed. In Alpha v.1.0.6_03 Obsidian is created from water colliding with a lava spring. This "technique" can be used to manipulate water and lava or to harvest cobblestone and obsidian.

Lava's texture was changed in the 0.0.19a client update on June 20, 2009 and is now animated. Lava is luminous and a large lava flow is visible in the dark from quite a distance.

In the survival game mode, lava takes 5 of the player's hitpoints for every second he is exposed to it because it lights him on fire and is extremely hard to put out. It is not possible to drown in lava, but the damage the player takes while swimming inside the lava is often enough to kill the player within a second, even when constantly healing himself. In Indev, if the Hell theme is chosen, most water is replaced with lava.

In Infdev, the amount of damage has been reduced to a half of a heart being removed for every second the player is in lava, in addition to the damage from fire. It will however deal the full 5 hearts of damage if a lava block enters a square the player is in where there wasn't one before, such as placing one where the player is standing or from flowing lava entering the player's block. Lava is no longer present at the bottom of maps in this mode.

Lava can melt ice and snow, much like torches can, but melt a larger area.

As of Seecret Friday Update 9, buckets of lava can be used to fuel a Furnace for 100 smelt; however, the bucket itself will be consumed in the process. Do not right-click on the furnace while holding your lava bucket, as this will only create a lava spring on top of your furnace!

Items thrown into lava flows will disintegrate. Though most object burn instantaneously, obsidian takes a few seconds longer.

Lava will flow for a total distance of 3 blocks away from the source block. Just like water, lava will flow in a single line towards the nearest terrain depression within four blocks.

Using a redstone wire, a one-block lava flow can be redirected by supplying power to the spring block, which will cause it to reset the flow towards the now-nearest terrain depression. This is further elaborated in this thread. It however cannot be reversed.

This re-calculation is made because redstone wire when toggled changes the block from redstone(on), to redstone(off). whenever a block updates on any side of lava, the lava re-calculates where to flow, but does not cut off it's current direction of flow.

Spring
You can collect and place Lava blocks using a Bucket. Placing the Lava block will create a Lava spring. Sometimes lava flows will linger, this is apparently intentional, and it will stop lingering, given enough time. As with Water, you can only harvest still Lava blocks (aka springs), not the flowing lava coming from the blocks.

Using a bucket to scoop lava will leave a hole missing from the pool as the lava blocks won't refill  the space you took from. With Water, a space adjacent to two Springs will be filled with another spring, but this  does not work with lava. The amount of lava blocks in a created world is currently finite and cannot be increased without modding as of Alpha. However, if you do acquire lava blocks through modding, pools created by placing these blocks will refill themselves.

Trivia

 * Lava is only called lava once it reaches the surface, and is called magma when underground. As such, most of the 'lava' in Minecraft is actually magma.
 * When your character catches on fire from lava he/she looks like this: