Podzol

Podzol is a dirt-type variant block that appears in the Mega Taiga biome and its variants. Similarly to grass blocks and mycelium, it can only be obtained by digging it with a Silk Touch-enchanted tool; otherwise, it drops dirt instead.

Podzol appears to share traits with mycelium, in that it allows mushrooms to be placed on it no matter the light level, thus allowing the growing of giant mushrooms. However, unlike mycelium, it does not spread to adjacent dirt blocks. Saplings and other plants can be placed on it. Podzol seems to represent dead pine litter on top of dirt, as it is found under giant spruce trees only.

Trivia

 * Unlike other similar blocks, podzol will never spread to dirt blocks, nor will it turn into dirt if a solid block is placed on top of it, no matter how long the block remains on top of it. This is because podzol is a type of soil, and has the same Block ID as dirt, just a different data value.
 * Neither grass nor mycelium can grow on podzol.
 * In real life, podzols (also known as spodosols) are one of the twelve classes of soil classification, usually found in coniferous forests in wet, cold areas as well as warmer areas. The name comes from a Russian phrase meaning "under ash", since podzols usually have a dark layer atop a bleached-white one and look like ash when plowed up.
 * All flowers can be placed on top of podzol.
 * Sugar Cane can be planted on a podzol block located next to water.
 * Podzol can be picked up by Endermen.