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.

Contents 1 Properties 2 Uses 3 Typical analysis of perlite 4 Production trends 5 See also 6 References 7 External links

[edit] Properties

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 bulk density: around 1100 kg/m³ (1.1 g/cm³).
Typical expanded perlite bulk density: 30–150 kg/m³

[edit] Uses

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 and filter aids.

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 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.^[1]

Perlite is an excellent filter aid. It is used extensively in Australia and New Zealand as an alternative to diatomaceous earth. The popularity of Perlite usage in this application is growing considerably worldwide.

In 2007, estimated U.S. usage applications are shown in the following table:

portion	general usage[2]
60%	building construction products
14%	horticultural aggregate
11%	fillers
7.5%	filter aid
7.5%	other

[edit] 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)

[edit] Production trends

In 2005, Greece was the top producer of perlite with at least one-third world share followed by China, USA, Japan and Turkey.^[3]

The cost of perlite has varied since 2001.^[4]:

end of year	$ per t
2001	36.3
2002	36.5
2003	38.2
2004	41.8[2]
2005	40.5[2]
2006	42.9
2007	51.6

[edit] See also

• Vermiculite (Many expanders of perlite are also exfoliating vermiculite and belong to both trade associations)
• Diatomite (used for filter-aids)
• Industrial minerals
• Mortar (firestop)

[edit] References

1. ^ Emulsion explosive composition containing expanded perlite United States Patent 4940497
2. ^ ^{a b c} http://minerals.usgs.gov/minerals/pubs/commodity/perlite/mcs-2008-perli.pdf
3. ^ Reported by the British Geological Survey
4. ^ "Perlite". U.S. Geological Survey Mineral Commodity Summaries,: 122–123. January 2006. [1]. 

[edit] External links

Wikimedia Commons has media related to: Perlite

• The Perlite Institute
• Mineral Information Institute - perlite