Silty clay is not clay. But I could make a reaction to remedy that, to split it into sand and clay. Just as an example.
The way that people tend to get clay from soil is a process that is basically mixing the silty/sandy clay in a container of water, until they get a very runny mixture of mud, and letting it settle, before draining off the clay slurry that rises to the top. You keep doing this, an then you let it evaporate a bit, before you strain it through cloth.
Perhaps a reaction that needs to use fibre/wool cloth in addition to the silty/sandy/loam clay to represent this? Might be too much to ask them to use water in the reason as well. I also imagine that ONLY Sandy Clay would give you Sand and clay, (would need bag for sand of course). You really should not get Sand from Loam/Silt. Maybe a bag of dirt instead, and you can turn bags of dirt into Dirt 'boulders'?
Maybe I'm thinking into Clay and sand and dirt too much.
