It depends on the type of shale. There are very soft shales sometimes called claystone that are little more than highly compressed clay. They revert back to clay in a hurry.

I am working on a project now with good Devonian Age shale (250 mil years old) that is very hard and makes great road base. We built a road with 18" of this stuff and it can carry very heavy trucks.


Bang on the shale you plan to use with a hammer. If it doesn't break easily its probaly good.