Perlite

For the two-phased structure in steel, see pearlite.

File:PerliteUSGOV.jpg

Expanded perlite

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.

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 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.

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, 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:

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

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)

Production trends

File:2005perlite.PNG

Perlite output in 2005

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

The cost of perlite has varied since 2001.:

end of year	Price in the US $ per t
2001	36.3
2002	36.5
2003	38.2
2004	41.8
2005	40.5
2006	42.9
2007	51.6
2008	60.0

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)

External links

• The Perlite Institute
• Mineral Information Institute - perlite
• Perlite in Turkey World %68 Deposits in Turkeycs:Perlit