Pumice ( //), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. It is typically light colored. Scoria is another vesicular volcanic rock that differs from pumice in having larger vesicles, thicker vesicle walls and being dark colored and denser.
Pumice is created when super-heated, highly pressurized rock is violently ejected from a volcano. The unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization. The depressurization creates bubbles by lowering the solubility of gases (including water and CO2) that are 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 depressurization freezes the bubbles in a matrix. Eruptions under water are rapidly cooled and the large volume of pumice created can be a shipping hazard for cargo ships. The pores of pumice and pumicite can have sizes from a wide range. Namely, the size of the pores can be as large as parts of micrometre (μm) and more rough pores with sizes up to 2–3 mm. The main difference between pumice and the pumicite is in the size of the grains. More specifically, the material with grain size of 2 mm or larger (up to large blocks) is classified as pumice. On the other hand, the material with size of grains smaller than 2 mm (including the fine dispersed material) is classified as pumicite.
Pumice is igneous rock with a foamy appearance. The name is derived from the Latin word "pumex" which means "foam" and through history has been given many names because its formation was unclear. In former times it was called "Spuma Maris", meaning froth of the sea in Latin, because it was a frothy material thought to be hardened sea foam. It was also known as "écume de mer" in French and “M
Pumice is igneous rock with a foamy appearance. The name is derived from the Latin word "pumex" which means "foam" and through history has been given many names because its formation was unclear. In former times it was called "Spuma Maris", meaning froth of the sea in Latin, because it was a frothy material thought to be hardened sea foam. It was also known as "écume de mer" in French and “Meerschaum” in German for the same reason. Around 80 B.C., it was called "lapis spongiae" in Latin for its vesicular properties. Many Greek scholars decided there were different sources of pumice, one of which was in the sea coral category.
Pumice can be found all around
Pumice can be found all around the globe deriving from continental volcanic occurrence and submarine volcanic occurrence. Floating stones can also be distributed by ocean currents. As described earlier pumice is produced by the eruption of explosive volcanoes under certain conditions, therefore, natural sources occur in volcanically active regions. Pumice is mined and transported from these regions. In 2011, Italy and Turkey led pumice mining production at 4 and 3 million tonnes respectively; other large producers at or exceeding a million tonnes were Greece, Iran, Chile and Syria. Total world pumice production in 2011 was estimated at 17 million tonnes.
There are large reserves of pumice in Asian countries including Afghanistan, Indonesia, Japan, Syria, Iran and eastern Russia. Considerable amounts of pumice can be found at the Kamchatka Peninsula on the eastern flank of Russia. This area contains 19 active volcanoes and it lies in close proximity with the Pacific volcanic belt. Asia is also the site of the second-most dangerous volcanic eruption in the 20th century, Mount Pinatubo, which erupted on June 12, 1991 in the Philippines. Ash and pumice lapilli were distributed over a mile around the volcano. These ejections filled trenches that once reached 660 feet deep. So much magma was displaced from the vent than the volcano became a depression on the surface of the Earth. Another well-known volcano that produces pumice is Krakatoa. An eruption in 1883 ejected so much pumice that kilometers of sea were covered in floating pumice and in some areas rose 1.5 meters above sea level.
Europe is the largest producer of pumice with deposits in Italy, Turkey, Greece, Hungary, Iceland and Germany. Italy is the largest producer of pumice because of its numerous eruptive volcanoes. On the Aeolian Islands of Italy, the island of Lipari is entirely made up of volcanic rock, including pumice. Large amounts of igneous rock on Lipari are due to the numerous extended periods of volcanic activity from the Late Pleistocene (Tyrrhenian) to the Holocene.
Chile is one of the leading producers of pumice in the world. The Puyehue-Cordón Caulle are two coalesced volcanoes in the Andes mountains that ejected ash and pumice across Chile and Argentina. A recent eruption in 2011 wreaked havoc on the region by covering all surfaces and lakes in ash and pumice.
Kenya, Ethiopia and Tanzania have some deposits of pumice.
The mining of pumice is an environmentally friendly process compared with other mining methods because the igneous rock is deposited on the surface of the earth in loose aggregate form. The material is mined by open pit methods. Soils are removed by machinery in order to obtain more pure quality pumice. Scalping screens are used to filter impure surficial pumice of organic soils and unwanted rocks. Blasting is not necessary because the material is unconsolidated, therefore only simple machinery is used such as bulldozers and power shovels. Different sizes of pumice are needed for specific uses therefore crushers are used to achieve desired grades ranging from lump, coarse, intermediate, fine and extra fine.
Pumice is a very light weight, porous and abrasive material and it has been used for centuries in the construction and beauty industry as well as in early medicine. It is also used as an abrasive, especially in polishes, pencil erasers, and the production of stone-washed jeans. Pumice was also used in the early book making industry to prepare parchment paper and leather bindings. There is high demand for pumice, particularly for water filtration, chemical spill containment, cement manufacturing, horticulture and increasingly for the pet industry. The mining of pumice in environmentally sensitive areas has been under more scrutiny after such an operation was stopped in the U.S. state of Oregon, at Rock Mesa in the southern part of the Three Sisters Wilderness.
A good soil requires sufficient water and nutrient loading as well as little compaction to allow easy exchange of gases. The roots of plants require continuous transportation of carbon dioxide and oxygen to and from the surface. Pumice improves the quality of soil because of its porous properties, water and gases can be transported easily through the pores and nutrients can be stored in the microscopic holes. Pumice rock fragments are inorganic therefore no decomposition and little compaction occurs. Another benefit of this inorganic rock is that it does not attract or host fungi or insects.
A good soil requires sufficient water and nutrient loading as well as little compaction to allow easy exchange of gases. The roots of plants require continuous transportation of carbon dioxide and oxygen to and from the surface. Pumice improves the quality of soil because of its porous properties, water and gases can be transported easily through the pores and nutrients can be stored in the microscopic holes. Pumice rock fragments are inorganic therefore no decomposition and little compaction occurs. Another benefit of this inorganic rock is that it does not attract or host fungi or insects. Drainage is very important in horticulture, with the presence of pumice tillage is much easier. Pumice usage also creates ideal conditions for growing plants like cacti and succulents as it increases the water retention in sandy soils and reduces the density of clayey soils to allow more transportation of gases and water. Addition of pumice to a soil improves and increases vegetative cover as the roots of plants make slopes more stable therefore it helps reduce erosion. It is often used on roadsides and ditches and commonly used in turf and golf courses to maintain grass cover and flatness that can degrade due to large amounts of traffic and compaction. With regards to chemical properties pumice is pH neutral, it is not acidic or alkaline. In 2011, 16% of pumice mined in the United States was used for horticultural purposes.
Pumice is widely used to make lightweight concrete and insulative low-density cinder blocks. The air filled vesicles in this porous rock serves as a good insulator. A fine-grained version of pumice called pozzolan is used as an additive in cement and is mixed with lime to form a light-weight, smooth, plaster-like concrete. This form of concrete was used as far back as Roman times. Roman engineers utilized it to build the huge dome of the Pantheon with increasing amounts of pumice added to concrete for higher elevations of the structure. It was also commonly used as a construction material for many aqueducts. One of the main uses of pumice currently in the United States is manufacturing concrete. This rock has been used in concrete mixtures for thousands of years and continues to be used in producing concrete, especially in regions close to where this volcanic material is deposited. New studies prove a broader application of pumice powder in the concrete industry. Pumice can act as a cementitious material in concrete and researchers have shown that concrete made with up to 50% pumice powder can significantly improve durability yet reduce the greenhouse gas emissions and fossil fuel consumption.