Mother Earth® Perlite & Coarse Perlite 4FtIn Store Location: @Outside Mother Earth Perlite & Coarse Perlite Mother Earth Perlite is naturally occurring siliceous rock that expands up to 20 times its original volume when heated to 1600 F. This kilning process is very similar to popping popcorn and produces a growing media that is sterile and has a neutral pH of 7. 0. The exceptional physical properties of this perlite make it tops in the perlite world for adding porosity to soil and soilless