Pumice Stone

Pumice is a type of extrusive volcanic rock, produced when lava with a very high content of water and gases is discharged from a volcano. As the gas bubbles escape, the lava becomes frothy.  When this lava cools and hardens, the result is a very light rock material filled with tiny bubbles of gas.  Commonly it is light-colored, indicating that it is a volcanic rock high in silica content and low in iron and magnesium, a type usually classed as rhyolite. Pumice is mined through open pit and quarrying methods. Extraction and processing methods vary, depending on the end use. It can be cut into blocks or crushed.

The density of the powdered material, amounts to between 2 and 3 kg/ dm3 and its bulk density, i.e. the density of the loosely piled material, amounts to between 0.3 and 0.8 kg/dm3. In other words, pumice is very light. Pumice particles are either round or angular and measure up to 65 mm in diameter.

The size of pumice particles ranges from superfine powder (0-2 mm) to sand (2-8 mm) to gravel (8-65 mm). The particle porosity can reach 85% and only 15% of the total volume consists of solid material. Its high porosity gives pumice good thermal insulating properties and makes it very light.



Applications for Pumice

Pumice is widely used to make lightweight construction materials such as concrete or insulative low-density cinder blocks. When used as an additive for cement, a fine-grained version of pumice called pozzolan is mixed with lime to form a light-weight, smooth, plaster-like concrete. This form of concrete was used as far back as Roman times.