Perlite is a naturally occurring siliceous rock that has been pulverized into very small particles. When it is heated, the particles undergo a physical expansion. It will take up 10 times its original volume when heated to 1000 degrees Fahrenheit.
When perlite is added to potting soil, it makes the soil light and improves ventilation in the root zone by providing many interstices for air and water. This improves drainage in heavy soils that are prone to run-off, as well as aeration of coarser textured clay-type soils which have more large pores than finer textured loams. Because perlite also has a high moisture holding capacity it increases the ability of soil to retain water, thereby increasing the total volume of soil available for uptake by plants. This also improves the stability of soil structure and reduces erosion. Perlite, unlike vermiculite or expanded clay-type soils, does not change pH levels.
Perlite can be used on its own as a potting mix or as an amendment to other mixes such as those containing peat moss or vermiculite in order to improve plant nutrition and reduce potential for plant disease. It also provides a surface of adhesion for roots that pokes through the soil when plants are planted in containers and thus assists with root development and establishment. Perlite is also an excellent source of calcium, a nutrient for plants and is used to support healthy plant growth, roots development, and plant tissue strength.
This mineral is commercially sold in bulk forms as mineral wool or perlite. The prices depend on the grain (small particles) size and process of making the product (e.g., air-dried or vacuum-dried). The air-dried perlite contains about 30% moisture content. This means that it has been heated at high temperatures (1000 °F) to drive off all water from being present in the otherwise dry products. After drying, this product has a relatively low specific weight due to the small size of its particles. Perlite is marketed by power and pelletized forms. The prices of the two products are similar. The price differences arise from elsewhere rather than product cost, as the power perlite offers some unique advantages over the pellet form.
The main consumer markets for perlite are:
Perlite is an excellent growing medium for germinating seeds and rooting cuttings, or as a soil amendment to increase or maintain moisture, promote drainage, and aerate soils. It has good water-carrying capacity, it will not compact under heavy loads like clay soils do. It will hold water, provide aeration for root systems and at the same time promote drainage.
Perlite is made of aluminum silicate, and it's available in several different grades. Perlite that has been crushed into very small pieces is known as blasting sand or scoria. This type of perlite is often used for insulating purposes and as a filter for exhaust gases in industrial processes. The size of perlite ranges from dust-sized particles to golf ball-sized pieces. Crushed perlite is actually more common than large chunks or aggregates of the mineral, particularly when used as a growing medium component.