Nylium

Nylium is a variant of netherrack that generates in the Nether. It has two variants: warped nylium and crimson nylium.

Natural generation
Warped nylium generates in the warped forest biome, and crimson nylium generates in the crimson forest biome.

Breaking
Nylium only drops itself when mined with a pickaxe enchanted with Silk Touch; otherwise, it drops netherrack. Nylium can also be picked up if dropped by an Enderman.

Post-generation
bone meal on netherrack that is placed next to or adjacent to warped or crimson nylium transforms the netherrack into nylium of that type. No block can be above the netherrack during this process. This transformation can also be done by activating a dispenser with bone meal directly into that netherrack block.

Usage
Similar to grass blocks and mycelium, nylium decays (immediately on a random tick) into netherrack when an opaque block is placed above it. However, unlike grass blocks and mycelium, it does not decay underneath water and lava.

Like mycelium and podzol, mushrooms can remain on nylium blocks in any light level. Huge mushrooms can be grown by using bone meal on mushrooms planted on nylium.

Fungi can likewise be grown into huge fungi using bone meal, though the fungus must be placed on the same type of nylium, or the bone meal will not even be consumed.

Similar to grass blocks, the player can apply bone meal to nylium. This nylium, along with nearby nylium, generate vegetation that occurs in their native biome (crimson nylium generates mostly crimson forest vegetation and warped nylium generates mostly warped forest vegetation).

Note Blocks
Nylium can be placed under note blocks to produce "bass drum" sound.

ID
{{ID table {{ID table
 * showblocktags=y
 * showforms=y
 * generatetranslationkeys=java
 * displayname=Crimson Nylium
 * spritetype=block
 * nameid=crimson_nylium
 * blocktags=enderman_holdable, mushroom_grow_block, nylium, mineable/pickaxe
 * displayname=Warped Nylium
 * spritetype=block
 * nameid=warped_nylium
 * blocktags=enderman_holdable, mushroom_grow_block, nylium, mineable/pickaxe
 * foot=1|showblocktags=y}}

{{edition|bedrock}}: {{ID table {{ID table
 * shownumericids=y
 * showforms=y
 * generatetranslationkeys=bedrock
 * displayname=Crimson Nylium
 * spritetype=block
 * nameid=crimson_nylium
 * id=487}}
 * displayname=Warped Nylium
 * spritetype=block
 * nameid=warped_nylium
 * id=488
 * foot=1}}

Trivia

 * The name is a portmanteau of "Nether" and "Mycelium", the name of the part of a fungus analogous to roots.