What is bentonite?

It's a clay that expands to severa times (20?) its original volume when wetted. It has incredible moisture holding capacity. They use it to seal leaking ponds.

I occasionally will get on a bentonite kitty litter binge and put it in a broadcast spreader putting it down as much as my eyesight can handle.
After so much the soil will kind of get crusty for a bit but not for long.

Does help water retention and extends the time it takes the lawn to wilt, in my sandy florida beach sand yard.