Two "expanded" minerals, plant vermiculite and perlite - have one thing in common - a porous structure which enables them to absorb enormous amounts of water. They are excellent soil conditioners and, unlike either organic matter or chemical conditioners, they remain practically unchanged for years.
Plant vermiculite and perlite are chemically inert and not readily attacked by soil acids or alkaline solutions. While more expensive than most other materials, they have very definite advantages. Clean, easy to handle, readily available and, for all practical purposes, sterile when they come out of the bag, they are convenient to use for seed starting or cutting propagation, for house plotting soils and for small garden areas. If the material is to be visible at the soil surface I prefer vermiculite because it looks more like soil. The white color of Perlite produces a soil mixture that is less natural in appearance. Where the soil is to be used for lawn purposes this surface color factor is unimportant since the Perlite will be hidden by the grass.
Both perlite and vermiculite can be used in amounts up to one third the total volume of the soil. However, they need not be used as freely as sand. Relatively smaller amounts of either material will bring about noticeable improvement in a soil.