Dirt

Dirt is a basic block found abundantly in the Overworld. It is found at any altitude, and comprises the majority of the upper terrain layers in most overworld biomes. Dirt can be thought of as a filler block, used during world generation to fill gaps between resources and features and provide shaping material for terrain, but it can also be collected and utilized for building. Grass, snow, and mycelium can spread/collect over the top layer of Dirt blocks; mining these will drop ordinary Dirt blocks. Podzol cannot spread to dirt blocks, because it is a variant of the dirt block itself.

When a dirt block is adjacent to a grass block and is exposed to a light level of at least 4 (e.g. from torches or sunlight), it will eventually be converted into a grass block at random intervals (see grass for growth details). Mycelium spreads in similar fashion, but requires a light level of at least 9.

A variant of dirt, grassless dirt, is featured in the Mega Taiga, Mesa and Savanna biome. The only difference to regular dirt is that grass cannot spread to it. It can only be obtained with the /give command and has a data value of 1. Once the block is broken, it becomes normal dirt.

Coarse Dirt is an upcoming variation of dirt that will replace the grassless dirt in Mega Taiga, Mesa and Savanna biomes. As the coarse dirt block uses the same block ID and data value as the original grassless dirt block, even old worlds with the grassless dirt blocks should have them seamlessly change over to coarse dirt. Silk touch is not required to obtain coarse dirt.

Obtaining
Dirt will always drop a resource block, regardless of how it was mined. It may be mined by hand fairly quickly, but using a shovel will significantly speed up the process. Dirt has very low blast resistance, so TNT or Creeper explosions will clear sizable areas of it. But using explosions isn't a good idea since most of the dropped dirt will be destroyed by the explosion.

Usage
Dirt is generally considered an obstacle during mining, though it is nevertheless useful in Survival mode for quick temporary structures like walk ways, quick easy houses and pillar jumping; it is easily mined even without tools, large quantities are generally readily accessible, and hostile mobs can not generally attack through it. A player caught outside when night approaches, for example, can remain fairly safe by sealing themselves into a small dirt cavity, or pillar-jumping up 16 or 20 blocks.

Large dirt structures can even serve as shelter for extended periods, if lit sufficiently to prevent mob spawns. Dirt structures can be outfitted with Doors and any other creature comforts, the same as most other blocks. Players will usually replace the dirt with stronger blocks over time (if only for increased blast resistance) but the dirt serves to block mob lines-of-sight, and to lay out the arrangement of the building.

Dirt is also important for its ability to grow a variety of items. Saplings, sugar canes, and mushrooms can be planted directly in dirt (under appropriate conditions for each). Using a hoe on placed Dirt blocks will turn them into farmland blocks, enabling wheat seeds, pumpkin seeds, melon seeds, potatoes, and carrots to be planted on it. Farmland will revert to dirt unless something is planted on it or it is irrigated by nearby water.

Trivia

 * Dirt Blocks have the same texture on all six sides.
 * When the block is changed by a hoe, it becomes a block called Farmland obtainable with /give.