OK, Its not koi clay but it is bentonite or is that one of the same? I did a nature days class a while back and I found these interesting rocks in the creak. Once I picked them up I noticed that it was a type of clay which I've never seen before. I thought it was so interesting on the consistency and smoothness of it so, I put some in a bag to take home. I molded this little mouse on the way home and let it dry over night, no cracks or anything. Next day we had a fire going in the wood burning stove and I tossed it in and kept it in overnight. In the morning I was amazed that it actually fired. After some research I have established that it has to be bentonite. Fun stuff and been working on some more pieces. Yeah, I know I'm weird, It’s the little things in life that keep me going.