EXPANDED SHALE: Made from natural and ground to 1” to ½” range particles and then kiln fires. As it progresses through the kiln for 40 minutes at 2,000 degrees C, certain chemical processes take place in the silica content (60-70%) causing the material to expand. As the material cools, cavities are left after gases escape, leaving a porous lightweight chunk capable of absorbing water and releasing it slowly at a later time.
I recommend it to be used along with other organic soil amendments to loosen and aerate soil. It is also an excellent potting soil ingredient, especially when used with shredded coconut fiber and compost.