Perlite
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For the two-phased structure in steel, see
pearlite.
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.
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[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
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In
horticulture perlite can be used as a soil amendment or alone as a medium for
hydroponics or for starting
cuttings.