Perlite is not a trade name but a generic term for naturally occurring siliceous rock. The distinguishing feature which sets perlite apart from other volcanic glasses is that when heated to a suitable point in its softening range, it expands from ( 4 : 20 ) times its original volume.
This expansion is due to the presence of (2 – 6 ) % combined water in the crude perlite rock. When quickly heated to above 900Co the crude rock pops in a manner similar to popcorn as the combined water vaporizes and creates countless tiny bubbles which account for the amazing light weight and other exceptional physical properties of expanded perlite.
The expansion process also creates one of perlite's most distinguishing characteristics: its white color. While the crude rock may range from transparent light gray to glossy black, the color of expanded perlite ranges from snowy white to grayish white.
Color |
White |
Refractive Index |
1.5 |
Free Moisture, Max. |
0.5% |
PH |
6.5-8.0 |
Specific Gravity |
2.2-2.4 |
Bulk Density |
50-400 kg/m3 |
Grain Size |
0 -5 mm |
Softening Point |
871-1093 C° |
Fusion Point |
1260-1343 C° |
Specific Heat |
837 J/ kg k |
Thermal Conductivity At (24 C°) |
0.04 -0.06 W/K.M |
Physical properties
Chemical Composition wt%
Sio2 |
72 - 76 % |
Fe2O3 |
0.5 - 1.5 % |
Al2O3 |
7 - 11 % |
Na2O |
2.9 - 4 % |
K3O |
4 - 5 % |
CaO |
0.5 - 2.5 % |
MgO |
0.1 - 0.5 % |
TiO2 |
0.03 - 0.2 % |
H2O |
2 - 6 % |
