Pumice is an igneous rock that has a light-colored and extremely porous appearance. It has been used in various industries for centuries. The rock is known as pumicite in its powdered or dust form. The rock is made up of highly vesicular rough textured volcanic glass. The rock may or may not contain crystals.
The word pumice is derived from the Latin word “pumex,” related to the Latin word “spuma,” meaning foam. Pumice has been called “Spuma Maris” (froth of the sea) and “lapis spongiae” due to its vesicular properties.
Pumice erupts from magmas that are supercharged with gas and have a rhyolitic composition. Pumice also erupts from gas-charge magmas of basaltic or andesitic composition. Pumice has a very low specific gravity due to abundant vesicles and thin walls. Most pumice rocks have a specific gravity below 1, letting the rock float on water.
Pumice produced by island and subsea eruptions can sometimes float on islands for long periods or even up to years. It is so lightweight that it can be pushed around by the winds. Floating pumice is known as pumice rafts. The pumice rafts can damage the ships that sail through them.
The major elements inside pumice stones are silicon dioxide (76.2%), aluminum oxide (13.5%), ferric oxide (1.1%), ferrous oxide (0.1%), and sodium oxide (1.6%). It also contains water less than 1% of.
Pumice Rock Formation
Pumice’s appearance explains its formation. The vesicles on its surface are gas bubbles trapped inside the rock when the gas-rich frothy magma is rapidly cooled. The cooling process is so quick that atoms inside the melt don’t get time to arrange themselves into a crystalline structure.
A sudden pressure drop happens when magma breaks through the earth’s surface. This pressure drop releases high volumes of gas at high pressure. The powerful discharge shreds the magma, blowing it out like molten froth. The molten froth solidifies when airborne and falls back as pumice dust or rocks.
The pumice deposits, as a result, can be as big as homes or as small as dust particles. Some deposits can be as big as 100 meters.
The world has seen two major volcanic eruptions that have resulted in humongous pumice deposit formation. One happened at Mount Pinatubo, Philippines, in 1991, and the other at Mount Mazama Eruption (Crater Lake) 7,700 years ago.
The eruption at Mount Pinatubo ejected more than 1 cubic mile of material. The event at Mount Mazama Eruption (Crater Lake) made a towering column of pumice and ash that reached some 30 miles high.
Where is Pumice Found?
Pumice is a commonly found rock. Its reserves are located worldwide. The biggest producers are Italy, Turkey, Greece, Iran, Chile, and Syria. It is produced in large numbers because of its 100s of uses. The total world population was estimated to be 18 million tons in 2019.
- Asia: Afghanistan, Indonesia, Japan, Syria, Iran, and Eastern Russia
- Europe: Italy, Turkey, Greece, Hungary, Iceland, and Germany
- North America: Caribbean Islands, USA: Nevada, Oregon, Idaho, Arizona, California, New Mexico, and Kansas.
- South America: Chile and Argentina.
- Africa: Kenya, Ethiopia, and Tanzania.
Pumice is one of the most commonly used rocks found on earth. It is cheap but has many valuable uses. It is commonly used in the following applications.
- Pumice is mixed with concrete to produce lightweight concrete blocks. The pumice’s vesicular structure keeps the blocks’ weight in check, reducing the structural steel required for construction.
- Pumice is commonly used as a landscaping and horticulture rock.
- It is also used as a drainage rock and soil conditioner in plantings.
- Pumice’s most common use is in abrasives. It is used as an abrasive in pencil erasers, washroom cleaners, skin cleaners, polishing, snow-covered roads, a traction enhancer in rubber, and a fine-grained filter media.
- It is also used as a lightweight filler for pottery clay.
- Ancient Chinese doctors used ground pumice and ground mica to make calming tea to treat dizziness, nausea, insomnia, and anxiety disorders.
- Pumice stones are attached to handles to remove limescale, rust, and hard water rings from toilet bowls.