Plainsman A2. In spite of three times the normal rain fall this summer, its natural high impermeability made it shed almost all of the water. But there is a back story. When mined this clay was quite wet, about 10% moisture - some of the lumps were 100 lbs! The outer ones dried over a period of weeks and, in the process, fractured down to the inch-size you see here. But the inner section of the pile took years to dry out. By now it has broken down so fine that a completely dry sample put into water will slake in minutes to produce a smooth slurry.
In ceramics, the permeability of clay slurries and plastics determines the rate as which water can move through the matrix