What is Pumice Stone?
Pumice is a rock with the main characteristics of being light in color and very porous. Pumice is a type of igneous rock formed from the explosive eruption of a volcano. This rock is also known as silicate volcanic glass because it contains foam from gas bubbles with glass walls.
Pumice is most widely used as a lightweight concrete aggregate and as an abrasive in various industrial products. Pumice has a high porosity so that it can float on water.
Features of Pumice Stone
Pumice has high vesicular properties, contains a large number of cells (cellular structure) due to the expansion of the gas foam contained in it. The large number of pore spaces (vesicles) in pumice which is limited by thin walls makes this rock has a very low specific gravity.
Types, origins and uses of pumice
Pumice usually has a specific gravity of less than 1, making it able to float on water. In general, pumice is found as loose material or fragments in volcanic breccias. The minerals found in pumice are usually feldspar, quartz, tridymite, and cristobalite.
Pumice has chemical and physical properties, including: containing oxides of SiO2, K2O, MgO, CaO, Al2O3, SO3, Fe2O3, Na2O, TiO2, and Cl, LOI (Loss of Ignition) 6%, pH 5, specific gravity 0.8 gr/cm3, low sound transmission, 16.67% water absorption, fire resistance up to 6 hours, low thermal conductivity, and a fairly high ratio of compressive strength to load.
Various Types of Pumice
Most pumice comes from magma containing gases that have a rhyolytic composition. It is very rare for pumice to come from magma of basaltic or andesitic composition. An explosive eruption will release volcanic material into the air, then the material will be transported horizontally and will accumulate as pyroclastic rock.
This formation process makes pumice categorized as a type of external igneous rock. Other rock types that have the same physical structure and origin as pumice are pumicite, volcanic cinter, and scoria.
Based on the material of origin, the way of formation, and the distribution of the size of the particles (fragments), pumice can be classified into several types, namely:
- Pumice sub-area
- Sub-aqueous pumice
- new ardante pumice stone
- Pumice from redeposit
The presence of pumice is always associated with a series of Quaternary to Tertiary volcanoes. The spread of pumice in Indonesia generally covers the islands of Lombok, Sukabumi, Serang, and Ternate Island.
Origin of Pumice Stone
The pore spaces (known as vesicles) in pumice are an indication of how the rock was formed. Vesicles are actually gas bubbles trapped in rock during the rapid cooling of gas-rich magma.
The material which cools very quickly causes the atoms in it to be unable to arrange themselves to form crystals. This is what underlies the experts to categorize pumice as a mineraloid because it is composed of amorphous volcanic glass.
Below the Earth’s surface, magma contains several weight percent dissolved gases because they are under the influence of high pressure. This condition is similar to dissolved carbon dioxide in a closed bottle of carbonated drinks such as beer or soda.
If you shake the bottle of beer or soda and then open the bottle, the sudden release of pressure allows the gas to escape mixed with the foam. In this case, the gas mixed with the magma will come out through the volcanic vent in the form of liquid froth. Furthermore, the foam will quickly cool when in the air, and fall back to earth as pieces of pumice.
Large volcanic eruptions can release large amounts of volcanic material. The material can be of various sizes, from fine dust particles to large blocks of rock the size of a house.
Pumice Stone Benefits
Pumice is not as expensive as gemstones, but pumice has many uses. In the paint industry, pumice can be used as a non-skid coating, acoustic insulation paint, paint texture filler, and as flattening agents. In the chemical industry, pumice can be used as a filtration medium, chemical carrier, and trigger for sulfur matches.
In the metal and plastics industry, pumice can be used as a cleaner and polisher, vibratory and barrel finishing, pressure blasting, electro-plating, and glass and glass cleaner. In the cosmetic industry, pumice is used as a dental polish and filling, as well as for skin leveling. In the compounder industry, rubber, and electronics, this rock can be used as hand soap powder, eraser, and circuit board cleaner.