Pumice is a porous, spongy, formed as a result of volcanic events, resistant to physical and chemical factors, glassy volcanic rock. In other words, pumice stone can be called as a very porosis volcanic rock glass. According to TS 3234 standard pumice is defined as a substance that is unconnected to each other porous, sponge-looking silicate-based, unit weight usually less than 1 gr/cm³, hardness is approximately 6 according to the Mohs scale, glassy texture.

During the formation, Pumice contains numerous pores from the macro scale to micro scale because of the abrupt abandonment of the inner gases and sudden cooling of the structure. Permeability is low, heat and sound is rather high due to non-aligned pores ( especially micro-pores), generally. Pumice is seperated from the similiar glassy volcanic rocks ( such as perlite, obsidian, pumice pearlitic) by some distinctive pores. Practically, seperated from these by colour, porosity and lack of crystal water. It is most widely-confused with perlite by colour similarity/proximity and chemical composition, in some cases it could be harder to differentiate from perlite. It can be distinguished from the transitive rocks which could be called as Perlit with Pumic/ Pumtic Perlit or Pearlitic Pumic by petrographic analysis, and pore structure. Pores are not related to each other mostly. Each pore from visibly size to microscobic size is isolated with a glassy membrane. Because of that, it is a light, floating for a long time, isolation rock. According to Mohs scale its hardness is 5-6. Chemically, 75 percent of silica content can be participated in.

Pumice stone overview

General Chemical Composition of Pumice

60-75% SiO2
13-17% Al2O3
1-3% Fe2O3
1-2% CaO
7-8% Na2O-K2O
trace amounts of TiO2 and SO3

SiO2 ratio that the rock contains in gives abrasive property to rocks. So it a chemical structure that abrasives steel easily. Al2O3 composition gives high strength to heat and fire. Na2O and K2O are known as the minerals that shows reaction properties in the textile industry.

Our country has an important potential in terms of many industrial raw materials and underground sources. At the same time, pumice has a very important place among the mineral resources for our country which has 40% (more than7,2 billion m³) of world reserves that is around 18 billion m³.

Pumice Formation

The pumice formation is described in general as follows: Acidic magma is more viscous than basic magma and contains high silica as a comparison. At temperatures that basic magma is liquid, acidic magma is being at solid form. Therefore, when the volcanic activity seems acidic rocks and masses occurs by stopping magma flow. Natural pressure accumulations occurs as a result of obstruction in the volcanic chimney. This event shows the general characteristics activity of a volcano.

By increasing of pressure dissolved gases at magma starts to outbursts together with acidic material in the form of huge explosions. Sudden release of pressure creates a sudden expansion. In the meantime, it causes the sudden escape of insider volatile compounds. Following the volatiles, the behindhand melted global parts cools down quickly as soon as contacting atmoshphere. So pumice forms and after the volcanic activity, volcano crater occurs which usually transforms into the shape of the crater lake over time.

A general view of volcanic activity