Pumice: Solidified Frothy Lava

Pumice is an igneous rocks which  formed when lava cooled quickly above ground.  Little pockets of air can be seen in the rock . This rock is so light, that many pumice rocks  actually float in water. Pumice is actually a kind of glass unike other rocks which are  mixture of minerals. Because this rock is so light, it is used quite often as a decorative landscape stone.

By origin, Pumice is a is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It is formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid cooling and rapid release of pressure. This release of pressure creates bubbles by lowering the solubility of gases (including water and CO2) dissolved in the lava, causing the gases to rapidly exsolve (like the bubbles of CO2 that appear when a carbonated drink is opened). The simultaneous cooling and pressure release freezes the bubbles in the matrix.

Economic Uses

Pumice is  used extensively to make lightweight concrete or insulative low-density breeze 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  in Roman times. Roman engineers used it to build the huge dome of the Pantheon and as construction material for many aqueducts.

It is also used as an abrasive, especially in polishes, pencil erasers, cosmetic exfoliants, and the production of stone-washed jeans. “Pumice stones” are often used in beauty salons during the pedicure process to remove dry and excess skin from the bottom of the foot as well as  to remove calluses. It was also used in ancient Greek and Roman times to remove excess hair. Finely ground pumice is added to some toothpastes and heavy-duty hand cleaners (such as Lava soap) as a mild abrasive. Pumice is also used as a growing substrate for growing horticultural crops.Its porous nature makes it a natural for filters.

In some aspects Pumice is  like scoriain that both are frothy, lightweight volcanic rocks, but the bubbles in pumice are small

Pumice Desert - 1

and regular and its composition is more felsic than scoria’s.Scoria differs from pumice in being denser. Pumice is  glassy and scoria is  lava with microscopic crystals.

 Pumice differs from obsidian in that obsidian is all glass and lacks the extensive vesicles of pumice. Most pumice is acidic/felsic in composition associated with rhyolite since those lavas tend to have more volatiles, but intermediate and basic varieties are known to occur. Scoria is a much heavier ropey volcanic rock with larger but less prolific vesicles than pumice.

Pumice Islands 

Some ocean  volcanoes have produced what are known as pumice rafts, which are actual floating mini islands made of rock. These pumice islands can be there for years floating along the ocean currents. Some may have been responsible for the distribution of island hopping animals and plants of the Pacific Ocean. Some pumice islands were found with plants actually growing on them.

Links and Sources:

Wikipedia, Rocks Hounds, Mineral Galleries

About Rashid Faridi

I am Rashid Aziz Faridi ,Writer, Teacher and a Voracious Reader.
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2 Responses to Pumice: Solidified Frothy Lava

  1. very nice to see on the subjects of LAVA I want to discuss in detail regarding lava , LAVA IS LIFE the elements that are present are the by products of not only sun air water earth and ether but lava plays vital role bringing life on the planet where exactly molten lava is nothing but fire at 2900 degrees c where it comes to contact through earth by pumping her molten lava on any planet will bring reaction with outer layer of earth core layer with sunlight and space where life comes with water life has formed in the oceans of sea .


  2. Pingback: Classification of Igneous Rocks | Rashid's Blog

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