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Apr 5, 2010

Perlite Rock - Properties and Uses

Perlite rock is a naturally occurring volcanic glass, which contains a relatively high amount of water. Its formation is typically by the hydration of obsidian. Occurring naturally, it is quite unusual in that it greatly expands when it is heated sufficiently. This makes it extremely lightweight and it has very many commercial uses, being mined industrially all over the western region of North America, as well as in many other countries around the world. There is a lack of detailed information regarding the world perlite production, but it appears to be abundantly available and so hopefully will be for many decades in the future. It's properties were known for many years, but it was not until 1949 that an institute was founded and this unusual and unique rock was mined for its countless commercial value.

When perlite rock reaches a temperature of around 850 - 900 degrees C, it softens (because it is actually a glass). The water which is trapped within the structure of the rock vaporises and escapes, which causes the expansion up to 20 times its original volume. The process is similar to that of popping corn. The perlite rock is bright white after expansion, because of the reflectivity of the millions of bubbles trapped within it. This also contributes to its unique lightness. Whereas unexpanded perlite rock will have a bulk density of somewhere around 1100kg/m3, once expanded it will typically have a bulk density of 30 - 150 kg/m3.

Because of its low density and the relative cheapness of perlite rock there have been many commercial applications developed for its use. The construction and manufacturing industries use it extensively in lightweight mortars, plasters and insulation, as well as for ceiling tiles and a variety of filter aids.

The horticultural industry use perlite as a soil additive or it can actually be used alone for the propagation of cuttings. Its lightweight properties make it ideal for adding to other peat and composts where it helps to maintain moisture and provide aeration. It is weed free, sterile and has a neutral pH value making it invaluable in the horticultural industry, both commercial and in the home for private use. It is present in many potting compounds and composts in today's market.

The fire resistant properties of perlite rock make it extremely useful in foundries, and as a fire stop in mortar and ceramics. It is also in use within the explosive industry. Another growing usage of perlite is as a filter aid for swimming pools and municipal systems. It is ideal for this type of use as it is classified as chemically inert.

It is estimated that around 60% of the perlite produced in the USA is used in some form by the construction industry. Of the remaining 40%, around 14% is used for horticultural products, and the remainder is used as fillers, filter aids and other uses. The majority of perlite uses are for the expanded form, although there are occasions when the original or 'raw' perlite rock is used.




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