When mined, it has rather a lot of trace mineral ions already adsorbed so it is often used as a trace mineral amendment. It holds water well but also passes air freely. It shares that characteristic with the open-pore forms of agricultural pumice. I use it in place of pearlite. It is at least as good for encouraging drainage but doesn't float out the way pearlite does.
Some hydroponic growers use it exclusively.
It is a great equalizer. A recent edition of the CSSA journal reported cacti and tender herbs growing close together in a high rainfall area rooted only in diatomaceous earth. The drainage and porosity kept the cactus roots from rotting while the water holding ability kept the herbs from drying. The mineral holding ability prevented all nutrients from being washed away.