Mystery fairy dust in the shop

The purpose of this thread is to figure out what the 50 gallons of dirt stored in buckets in the shop is there for.
It's about 98° outside right now so I'm finding some indoor stuff to do which today involves cleaning up our work area.
Underneath one of the work benches is a sizeable stack of plastic containers all of which contain a very fine, almost powdery sand. This dust doesn't especially special as I'm finding lots of twigs and rocks mixed in with little bits of grass, but for someone to go through the effort of bringing all of it inside there must be something valuable here.

For the moment a few handfuls are doing a fine job of soaking up some oil.

I'm hoping that someone who has been here will know what these buckets were for.
Thanks permies!

Hey Josh. Do you think it might be clay? I'd try mixing a bit with water and see if you can roll out a sausage.

The "metal splinters" are for the rocket mass heater casting stuff. They are a special type of aggregate.

The buckets of dust: A kind of clay and fine silt mix. they can go on top of the berm shed on a rainy day. Keep the buckets!

Ok we'll leave those alone for now.

Just because you asked this is the most it will roll out, as curved around as it will go.