Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently. It is an industrial mineral and a commercial product useful for its light weight after processing.
When it reaches temperatures of 850–900 °C, perlite softens (since it is a glass). Water trapped in the structure of the material vapourises and escapes, and this causes the expansion of the material to 7–16 times its original volume. The expanded material is a brilliant white, due to the reflectivity of the trapped bubbles. Unexpanded ("raw") perlite has a bulk density around 1100 kg/m³ (1.1 g/cm³), while typical expanded perlite has a bulk density of about 30–150 kg/m³.
Due to its low density and relatively low price, many commercial applications for perlite have developed. In the construction and manufacturing fields, it is used in lightweight plasters and mortars, insulation, ceiling tiles, in horticulture and as filter aid.
In horticulture, perlite can be used as a soil amendment or alone as a medium for hydroponics or for starting cuttings. When used as an amendment it helps prevent water loss and soil compaction.
Perlite is an excellent filter aid. It is used extensively as an alternative to diatomaceous earth. The popularity of perlite usage in this application is growing considerably worldwide.
Small quantities of perlite are also used in foundries, cryogenic insulation, as a lightweight aggregate in mortar (firestop) and in ceramics as a clay additive. It is also used by the explosive industry.
In 2007, estimated U.S. usage applications are shown in the following table:
Typical analysis of perlite
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