Mycelium

Mycelium is a block similar to a Grass Block, but is only found natively in Mushroom Island Biomes. It can grow over adjacent dirt blocks, similar to grass.

Appearance
Mycelium looks and acts very similarly to grass, though with a particle effect that resembles tiny spores being released constantly from the surface. This effect persists even when covered in snow; the sides will use the same texture as snow-covered grass, with the spores being the only way to visually tell them apart.

Features
Like grass, Mycelium yields a dirt block when harvested. The Silk Touch enchantment can be used to acquire Mycelium blocks.


 * Mushrooms can remain on Mycelium blocks even in high light levels, unlike other blocks that generally break Mushrooms (dropping them as items) during block updates in high light.
 * Huge Mushrooms can grow on Mycelium (but can also grow on dirt and grass).
 * Mycelium cannot be tilled with a hoe to make farmland, and saplings and flowers cannot be planted in it.
 * Mycelium is found exclusively in Mushroom Island biomes, unless transplanted via the Silk Touch enchantment or placed in Creative Mode.
 * Mycelium does not limit hostile mob spawning or allow Mooshrooms to spawn; both these traits are exclusive to the Mushroom Island biome, not to Mycelium.

Spread
Mycelium is only found naturally in Mushroom Island biomes, but it can spread anywhere or be pushed anywhere with a piston.

Mycelium spreads in exactly the same way as grass: A mycelium block can spread to any dirt block within one space above, one sideways, or three down. The mycelium needs light level 9+ above it and the dirt needs light level 4+ above it, and must not be covered by any light-impeding block i.e. water, ice, slabs, stairs, farmland, or any opaque block. Mycelium also dies under the same conditions as grass: when covered by one of the light-impeding blocks above and the light level at that block is below 4.

Mycelium and grass do not replace one another; whichever arrives on the dirt first will remain. If there is a sapling or flower on a block of dirt when mycelium spreads to it, the plant will pop out and drop as an item. Pumpkins and melons will not spawn on mycelium, even if the stalk is otherwise healthy.

Generated caves and ravines in a Mushroom Island biome will not remove mycelium, often leaving a thin layer over a ravine or 'bars' of mycelium covering a cave.

While mycelium cannot take over farmland, any block that reverts (perhaps because a pumpkin grew on it) is vulnerable not only to visibly adjacent mycelium blocks, but also to mycelium under adjacent partial blocks (e.g. farmland, slabs, stairs) or transparent blocks. To restrain mycelium from spreading into (or out of) an area, one can surround the area in a ring of cobblestone (or any other opaque non-dirt block) inset in the ground and ensure mycelium is not buried under any partial or transparent blocks.

When harvested, Mycelium drops one dirt block, but a tool enchanted with Silk Touch can harvest mycelium.

Trivia

 * It is a common misconception that only mooshrooms can spawn on mycelium. This is not true; friendly and hostile mobs can spawn on mycelium just as on any other block. It is the mechanics of the mushroom biome that prevents other mobs from spawning. Relatedly, mycelium outside of a mushroom biome will not spawn mooshrooms.
 * The spore particle effect is called "townaura" in the game code. This may indicate that the gray particle effect was originally planned to mark the area of villages, along with the unused textures in terrain.png.
 * Mycelium is a popular alternative to grass in player's builds.
 * In real life, mycelium is the mushroom's nutrient gathering web of thin threads know as hyphae. The entire mushroom, from the mycelium to the cap is made entirely of hyphae.