|“||In the deep places of the world! And thither we are going against my wish. Who will lead us now in this deadly dark?||”|
–Boromir, son of Denethor, Fellowship of the Ring, Journey in the Dark
Caves and mining are a staple of Minecraft, and while Middle-earth places much less emphasis on the underground world, there is still plenty to find below the surface in any given biome. The underground world generates similarly across most of Middle-earth, and this page is intended to serve as a general overview for what you can expect to find underground. Anything additional - like biome-specific ore spawns, rock types, or structures - will be detailed on that biome's specific page.
On average, the ground level is around Y=70 in most biomes, with that number often being lower near bodies of water or in marshy biomes and drastically higher in hillier and mountainous biomes. Most of the space between the dirt layer on the surface of most biomes (which is absent or only semi-present in some) and the bedrock layer that generates at Y=1 will be stone, with pockets of dirt and gravel appearing with regularity. In certain biomes, like Gondor, there will be a thin layer of specialized rock between the dirt layer at the top and the stone layer beneath it, and pockets of that rock will generate underground.
Almost every biome is composed primarily of stone underground, and thus has ore distribution that is either identical to or an addition to the one that will be described below. The only exceptions to this rule are biomes in Mordor, which are composed of Mordor Rock beneath the surface, and as a result none of the ores below are present.
Caves in Middle-earth are very similar to the caves one would expect to encounter in vanilla, tunnel-like patches of air blocks that generate underground, often forming large, labyrinthine networks. All of the varieties of cave that can be found in the Overworld, from your basic caverns and pits to ravines and underground lakes. Both water and lava lakes can be found underground in Middle-earth, though they are far less common than they are in the Overworld. Indeed, caves in general are rarer in Middle-earth, especially ones that can be accessed from the surface. As in vanilla, streams of water and lava can be found regularly in caves, and additionally all caves below Y=10 are filled with lava.
However, caves in Middle-earth have two notable differences in structure from their vanilla counterparts. Stalactites and stalagmites generate regularly in caves, especially in larger ones, where they typically generate in clumps. In addition, caves in Middle-earth often contain cobwebs (to make up for the lack of abandoned mineshafts, most likely).
Mobs and Structures
In vanilla, caves are havens for all manner of monsters that usually come out at night (as well as for passive bats). Such monsters do not exist in Middle-earth, but in many biomes worse threats lurk underground in their stead - Orcs. Many regions are stalked by servants of the Shadow, who come out to hunt at night and slink back to their caves when the sun rises. These creatures can be found in unlit caves in any biomes they can spawn in at any time (and like in vanilla, bats can spawn alongside them).
This isn't a universal threat, however - players who ally themselves with evil factions need not fear encountering Orcs and their allies underground, and many biomes don't have Orcs spawning in them at all, meaning their caves are usually devoid of potentially-deadly mobs. Nonetheless, those who side with the Free Peoples should take care when journeying down into the darkness, especially in those regions that are thick with Orcs.
Middle-earth doesn't have nearly as many underground structures as the vanilla game does; most of the ones it does have are either small ruins that generate near the surface or biome-specific. The only traditional structure that can be found underground - albeit quite rarely - is the Orc Dungeon. Orc Dungeons can be found in any biome where Orcs are common, and can house Orcs of essentially any breed. They are simple structures composed of stone brick, containing nothing but Orcs, a few pillars, and stone chests with valuable Orcish loot. It is likely that these dungeons serve as field bases for tribes of Orcs to return to in the daytime, and in which to store their loot.
A wide variety of ores can be found underground in Middle-earth, including but certainly not limited to those found in vanilla. The following can be found at the rates detailed in most biomes, with exceptions being detailed on those biomes' pages.
Coal, copper, and tin can be found at Y=128 and below in the average biome, which makes it possible for them to generate on the surface in some biomes. Coal, as in vanilla, is the most common, generating at a higher rate than any other ore. Coal generates in veins of up to sixteen ore, and is a necessary resource for any player. Copper and tin are slightly less common, with a maximum ore size of eight; however, they're also quite useful, as they can be combined to make bronze.
Many more ores can be found a bit deeper underground, starting at Y=64. As in vanilla, iron can be found at that level and below at roughly half the rate of coal, and in Middle-Earth sulfur and nitre can be found at the same levels at significantly lower rates; all three generate in veins of up to eight. Rock Salt can also be found below Y=64, with the same chance of being generated as nitre or sulfur and a maximum vein size of twelve. Miners can also begin to find valuable gemstones at these levels - topaz and amethyst can be found in veins of up to six below Y=64, each generating at half the rate of nitre, sulfur, and rock salt.
More gems can be found below, with amber and opals generating uncommonly below Y=48 in veins of up to five. At Y=32 and below, silver and gold can be found in veins of up to eight. Silver is a bit more common than gold, generating at 3/2 the rate of its vanilla cousin; both are quite valuable. At the same Y-levels as silver and gold, miners might also stumble upon rubies and sapphires, which appear quite uncommonly in veins of up to four. Unlike in vanilla, lapis lazuli cannot be found in most regions of Middle-earth, and redstone cannot be found at all.
A few ores generate at the lowest levels of the world, often making them difficult to find due to the lava that fills the deepest of caves. The only low-level ores to spawn in most biomes are emeralds and diamonds, gemstones that shouldn't be confused with their vanilla counterparts, neither of which appear in Middle-earth. Emeralds can be found in veins of four below Y=24, and are slightly more common than diamonds, which also generate in veins of four, albeit only below Y=16.