Perlite

Furthermore, it is used in flower-soil-mixtures to decrease the density of the floor. Perlite possesses similar characteristics and application possibilities like vermiculite, but typically contains more oxygen and less water.
With the use of a “flow-and-drain” system, it can swim, if it is used loose. Perlite is a combination of granite, obsidian, pumice and basalt. This volcanic stone is melted naturally under high temperatures, a procedure that is called “fusionic metamorphosis”.