Black Lava Rocks by Plant Culture PH
Lava rock is formed by the action of volcanoes, bringing up molten rock from deep under the crust of the earth. The volcanic rock cools on contact with the air, complete with air pockets. In some cases it is so light that it floats on water. The porous air filled rock also has a high water holding capacity as the moisture will stick to the extra high surface area. In almost a complete contradiction, lava rock has very good drainage.