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Perlite

Perlite is an amorphous glass mineral of volcanic origin.

Typical analysis: 70-75% SiO₂, 12-15% Al₂O₃, Na₂O 3-4%, K₂O 3-5%, Fe₂O₃ 0,5-2%, MgO 0,2-0,7%, CaO 0,5-1,5% Loss On Ignition 3-5%

Properties: When it reaches temperatures of 850-900°C, perlite softens (since it is a glass) and water trapped in the structure escapes and this causes the expansion of the material to 7-15 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 gr/cm³).
Typical expanded perlite bulk density: 30-150 kg/m³

Due to the low density of expanded perlite it has many uses: Lightweight plasters and mortars, insulation, ceiling tiles. In horticulture it makes composts more open to air, while still having good water-retention properties; it makes a good medium for hydroponics.

See also

List of minerals

Vermiculite