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What is Pumice Stone

The Latin word Pumex, meaning “foam”, was used to derive the word pumice. Pumice is formed from volcanic matter and is a pyroclastic, igneous rock. Pumice is primarily composed of amorphous aluminium silicate (silicon dioxide), aluminium oxide, and trace amounts of other oxides, such as ferric and ferrous oxide, sodium oxide, calcium oxide, and magnesium oxide, although the chemical properties of pumice vary between deposits. Its mere appearance shows that it is high in silica content as it has a pale, light color, fluctuating from white to grey to green-brown. Apart from the silica content, its color also shows the lack of iron and magnesium in it. Pumice has two types of vesicles, tubular micro-vesicles, and spherical or sub-spherical vesicles, which provide pumice with a vesicular matrix structure. It is extremely porous and is the only rock which can float on water. However, once it has absorbed enough water it eventually sinks..

How Does Pumice Form?

The main source of pumice is explosive volcanic eruptions. It is formed when highly pressurized, burning liquefied rock, with its assimilated water and gases, deliriously erupts to the surface during volcanic eruptions. Further, the rock undergoes rapid depressurization which helps in forming the frothy, vesicle-riven structure. Along with this, depressurization which is carried out with rapid cooling, lowers the solubility of gases trapped in the liquefied rock, activating the development of bubbles, and resulting in the gases to be separated from the solid solution. The solidified foamy matrix of pumice is formed through rapid cooling which freezes the bubbles and traps them.  

The two vesicles in pumice along with the thin walls between them results in the rock having a very low specific gravity. The specific gravity of pumice is almost less than one which allows the rock to float on water. You can find large amounts of pumice floating on the surface of water. These pumice rocks are produced by some islands and subsea eruptions and with the help of wind these rocks are pushed far away from its origin. Sometimes pumice rocks float for long time periods.

Uses of Pumice

For the past few years, United States has had the largest use of Pumice in the production of lightweight concrete blocks and other lightweight concrete products. The vesicles in pumice remain partially filled with air while mixing it with concrete which results in less weight. The reduced weight of concrete blocks helps in reduction of structural steel requirements of a building. Apart from reducing the weight, the trapped air also helps in insulation.

The most frequent use of pumice is in landscaping and horticulture. Apart from acting as a decorative ground cover in landscaping and planters, pumice stones are used as drainage rocks. These rocks suck all the water, when the plants suffer from a dehydration period, the rocks provide them with water along with certain essential nutrients which helps plants grow. These rocks don’t decompose and so there will be no need of replacing them. The plants use pumice for daily essential nutrients while detoxifying themselves. Many vital nutrients are stored in the microscopic pores of pumice rock which aids in regulating fertilizer feedings. Apart from this, the pumice rock can be filled with nutrients before adding it to the soil. Furthermore, the pumice rock acts as a conditioner for the soil with increased aeration and drainage. Pumice rock also helps slacken the density of heavy clay garden soils, eventually helping the plants to get the water and air they want. Pumice has a lot of benefits for the soil and plants which include reduced crusting, cracking, flooding, shrink-swelling, holds the moisture in the soil, the pH of pumice is neutral, and it does not attract or host fungi, nematodes, or insects.

There are many other uses for pumice as well. It acts as a traction material on snow-covered roads and enhancer in tire rubber, furthermore, it is an absorbent in cat litter, a fine-grained filter media, and a lightweight filler for pottery clay. There are many more uses of Pumice due to its simple but unique properties.

Pumice in Soil

Pumice for plants has been proven to be a very useful discovery. Adding as little as 10 percent to your soil will yield fruitful results. In case of succulents, using half pumice is recommended. As mentioned above, you can use it straight out of its bag or you can fill it with the essential nutrients. Soaking the rock in nutrients for 24 hours is suggested.

Perlite vs Pumice

Perlite and Pumice are two almost same pebble like materials. Both have the same purpose to help aeration and water drainage for plants. Pumice is directly extracted while perlite is further heated which expands the perlite to 20 times its original volume. Perlite is lighter in weight than pumice and has a pure white color. Perlite is less expensive as compared to pumice however, perlite does not provide any nutrients to plants and its sole purpose is only drainage.

Pumice and perlite were shown to have similar physiochemical properties which subsequently translated into similar behavior in blended potting soil mixtures. It proved equally, if not even more effective in some ways than perlite. The unique structure of pumice and the sponge like material makes it special for the plants and trees as it helps them get the essential nutrients they want for a healthy growth. Its porous feature stores water and different nutrients which are released as per requirement of the plants and trees. Apart from all this, pumice is being used by many leading industries to create light weight concrete which reduces the price cost and improves the quality.


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