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.
Perlite softens when it reaches temperatures of 850–900 °C (1560-1650 °F). Water trapped in the structure of the material vaporises 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 (0.03-0.150 g/cm3).
Production and uses
Perlite is a non-renewable resource. The world reserves of perlite are estimated at 700 million tonnes. In 2011, 1.7 million tonnes were produced, mostly by Greece (500,000 t), United States (375,000 t) and Turkey (220,000 t). However, no information for China – a leading producer – was available.
Because of its low density and relatively low price (about US$50 per tonne of unexpanded perlite), many commercial applications for perlite have developed. In the construction and manufacturing fields, it is used in lightweight plasters and mortars, insulation and ceiling tiles.
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 has high permeability / low water retention and helps prevent 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. Perlite filters are fairly commonplace in filtering beer before it is bottled.
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 explosives industry.
In 2010, estimated perlite consumption in the US was as shown in the table:
|53%||building construction products|
The cost of unexpanded perlite has varied since 2001.:
|Price in the US
$ per t
Typical analysis of perlite
- 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)
- Expanded clay aggregate, an alternative lightweight filler for building materials
- Biochar, the large surface area of carbon molecules increases the soil structure, aeration, nutrient and water retention capacity. Biochar creates a healthy soil in which micro-organisms thrive
- Vermiculite, many expanders of perlite are also exfoliating vermiculite and belong to both trade associations
- Diatomite, used for filter-aids
- Industrial minerals
- Mortar (firestop)
- Perlite, USGS Mineral Commodity Summaries 2011
- Wallace P. Bolen Perlite USGS 2009 Minerals Yearbook
- Emulsion explosive composition containing expanded perlite United States Patent 4940497
- "Perlite". U.S. Geological Survey Mineral Commodity Summaries,: 122–123. January 2006. .
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