How common is it to have no lignite or bituminous coal in Dwarf Fortress?

I've started several fortresses now, and I've never encountered any lignite or bituminous coal. I've even prospected a couple maps (with DFHack) to see if it was merely out of reach, but unless prospect doesn't show these minerals, there has never been any in my maps.

Is this common, or am I doing something wrong?

Solution 1:

They are fairly commonly found in sedimentary layers, such as

• Sandstone
• Siltstone
• Mudstone
• Shale
• Claystone
• Rock salt
• Limestone
• Conglomerate
• Dolomite
• Chert
• Chalk

If you're running an older version of DF (31.19 or earlier), you can check what sort of layers are available on the embark site.

Keep in mind you can burn wood to make coal, though it is less efficient, wood is available aboveground in most biomes, and in caverns. You can also use magma smelters and forges to remove the need for most coal, the notable exception being steelmaking, which requires fuel no matter what.