40d:Stone layers

There are four layers of stone in Dwarf Fortress. Each has different types of of ore and gems available. Layers are extremely important in site selection because it determines what metals there are to work with. Layers also help in determining where to begin Exploratory mining depending on what is needed for the fortress.

Sedimentary

Appears in a lighter shade on the embark menu. Often includes coal, iron ore, and all but one of the flux stones, all the components for making steel. Never found in the same biome as igneous extrusive. Full to the brim with solid sexiness valuable and useful deposits. Only place to find bituminous coal and lignite, and iron ore in large clusters (magnetite). Good choice for Exploratory mining.

Metamorphic

Contains a small variety of ores, but tends to be rich in gems. Includes marble, the only non-Sedimentary flux. If there are no flux sedimentary layers Metamorphics can be useful in the early stages but the lack of weapon quality ore (besides copper and silver) make it a poor choice for full scale Exploratory mining in the early game.

Igneous Extrusive

Appears in a darker shade on the embark menu. It is likely to include obsidian and metal ores. It also indicates a good chance of liquid sexiness magma being present in some form or another. Never found in the same biome as sedimentary.

Igneous Intrusive

Like extrusive, also often contains liquid sexiness magma, but farther down typically. Often contains gold or copper ore. All Igneous layers can contain veins of Hematite a ore of iron.

Other Layers

Soil

Appears in brown on the embark menu. Useful for growing crops and storage, but provides no rock for building.

Magma

Not visible on the embark menu, unless you build directly on a volcano or enable it in init.txt. Both useful and fun dangerous.

Aquifer

Appears as a line of tildes(~) on the embark menu. This layer of wet stone can be used as a water source, but acts as a barrier to layers below it.