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 g/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 and filter aids. In horticulture it makes composts more open to air, while still having good water-retention properties; it makes a good medium for hydroponics. Perlite is also used in foundries and cryogenic insulations.