Man, I wish had time to contribute to this. This is all very beautifully executed, and makes me desire the day when the game looks like this.
Argh! too much school work, otherwise I'd isometrify my dwarf graphics set for this.
As a complete Rock Geek, this is something I've been mulling over for a while to try and find a way to do it right. I took some of your suggested textures, as well as a set of others, and added in a few others. Each category will have a generic greyscale stone texture, which we can apply colors to in order to create all the different stone types. Eventually, I'd like to have multiple textures of each category, which will be cycled through to create more natural-looking walls.
1. Flakey Sedimentary (Shale, Mica)
2. Grainy Sedimentary (Sandstone, Siltstone)
3. Clear Crystaline (Ruby, Rock Salt)
4. Opaque Crystaline (Obsidian, Bituminous Coal)
6. Smooth Igneous (Basalt, Rhyolite)
7. Coarse Igneous (Granite, Diorite)
7. Lusterous Metamorphic (Marble, Quartzite)
8. Foliated Metamorphic (Gneiss, Phyllite)
9. Nodular (Bauxite, Conglomerate)
10. Metalic (Hematite, Tetrahedrite)
I will comment that this is almost exactly the list Dwarfletter ended up with for its stone/soil tiles, though some are double duty. The nodular tile in particular ALWAYS makes good ore walls, for any ores that are or appear to be native metal, like gold, copper, and hematite. Most of the other metal ores are colorful oxides and crystals. It works very well at giving a colorful and detailed visual experience.
Saturday I MIGHT have some time to take a crack at some of these, if no one minds.