These are my planned soils (and as far down they go). I am going to try to make these produce "stones" from mining. The organic matter is very small pieces of plant matter normally found in soil (not entire leaves). I could potentially rename these to be "leaf bit" or similiar.
bark (top soil)
leaf (top soil)
pine needle (top soil)
twig (top soil)
humus (sedimentary)
loam (sedimentary)
peat (sedimentary)
chalk (all layers)
clay (all layers)
sand (all layers)
silt (all layers)
These are my planned undiggable stones (and when they first appear when digging down). They will appear is small clusters and have to be dug around.
sandstone (metamorphic)
siltstone (metamorphic)
limestone (igneous intrusive)
shale (igneous intrusive)
obsidian (igneous intrusive)
These are my planned metals (and when they first appear when digging down). They will be represented as single tile metal flakes in the soil (e.g. "copper flake") that can be mined out and turned into metal at a smelter.
aluminum (metamorphic)
copper (metamorphic)
gold (igneous intrusive)
iron (metamorphic)
lead (metamorphic)
nickel (metamorphic)
silver (igneous intrusive)
tin (metamorphic)
zinc (metamorphic)
These are my planned gems (and when they first appear when digging down). Instead of traditional gems, they are items that could be found in dirt and reasonably dug out by an ant. These are very small objects. They are closer to a single drop of sap turned into amber, not a large dinosaur fossil.
amber (metamorphic)
fossil (igneous intrusive)
petrified wood (igneous intrusive)
shell (sedimentary)