ok... i'll try to jump in on this one
Soils-
[INORGANIC:CLAY]
[USE_MATERIAL_TEMPLATE:STONE_TEMPLATE]
[STATE_NAME_ADJ:ALL_SOLID:clay][DISPLAY_COLOR:4:6:0][TILE:178]
[SOIL]
[SOLID_DENSITY:1600]
if you want it to be sugar just change the name to sugar... if that is also your sand then add a [SOIL_SAND] in there. Soils don't have boulders. The density controls how hard it is to mine, higher = longer. You can delete all of the stock soil layers and make up your own (and all the rock layers etc). I just like keeping in the stock stuff and changing the values/names since world gen runs more smoothly that way. But watch out for giving multiple entries the same name... if a noble fixates on "sugar" material and you have 5 of them it's either guess right or get alot of beatings. Color variations in the names would work well "white sugar"/"powdered sugar"/"brown sugar" etc.
example:
[INORGANIC:SUGAR_BROWN]
[USE_MATERIAL_TEMPLATE:STONE_TEMPLATE] -- or whatever template you set up or just put all the stats in without a template
[STATE_NAME_ADJ:ALL_SOLID:brown sugar][DISPLAY_COLOR:4:6:0][TILE:178]
[SOIL][SOIL_SAND] -- can be gathered for making "glass"
[SOLID_DENSITY:800] -- easy to cut through
Layers
[INORGANIC:SANDSTONE]
[USE_MATERIAL_TEMPLATE:STONE_TEMPLATE]
[STATE_NAME_ADJ:ALL_SOLID:sandstone][DISPLAY_COLOR:6:7:0][TILE:'#']
[SEDIMENTARY][AQUIFER][SEDIMENTARY_OCEAN_SHALLOW]
[IS_STONE]
[MELTING_POINT:12070]
There are 3 types of layer [SEDIMENTARY],[IGNEOUS_EXTRUSIVE] and [METAMORPGIC]
I don't know how the game would react to you making an entire custom layer set of stones with only one type; i.e. all [SEDIMENTARY]. But that would make for some interesting testing. I'd jut put all 3 tags in for all of your layer stones so that they appear everywhere.
Again, you can make up all your own stones and not use anything stock. Just make sure that whatever is your "flux" has the [REACTION_CLASS:FLUX] tag. As for not leaving boulders, that should be easy too just make it a [SOIL] and leave the [IS_STONE] out.
FIddle with the density for ease of mining.
example:
[INORGANIC:NOUGAT]
[USE_MATERIAL_TEMPLATE:STONE_TEMPLATE] -- again any template you make will work
[STATE_NAME_ADJ:ALL_SOLID:nougat][DISPLAY_COLOR:4:6:0][TILE:178]
[SEDIMENTARY][IGNEOUS_EXTRUSIVE][METAMORPHIC]
[SOIL] -- no boulders
[SOLID_DENSITY:1200] -- easy to cut through but stickier than brown sugar so slower
Tip: don't make your flux stones a soil.. that would be aggravating.
For boulders of a specific type, without that stone being in a layer, I'd use gems. If that's not what you're looking for then make it a mineral and clearly define where and how large the deposits are.