‘Perlite is an amorphous volcanic glass that has a relatively high water content. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently.’ – http://en.wikipedia.org/wiki/Perlite
When used within soil, Perlite makes composts more open to air, whle retaining its water-retention properties.
Perlite is formed from the following compounds:
* 70-75% silicon dioxide: SiO2
* 12-15% aluminium oxide: Al2O3
* 3-4% sodium oxide: Na2O
* 3-5% potassium oxide: K2O
* 0.5-2% iron oxide: Fe2O3
* 0.2-0.7% magnesium oxide: MgO
* 0.5-1.5% calcium oxide: CaO
* 3-5% loss on ignition (chemical / combined water)
We recommend using a soil mix of peat:perlite:sand to a ratio of 70:15:15.