Pumice (/ˈpʌmɪs/), calledpumicite in its powdered or dust form, is avolcanic rock that consists of extremelyvesicular rough-texturedvolcanic 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.[1][2]
Pumice is created when super-heated, highly pressurized rock is rapidly ejected from avolcano. The unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization. The depressurization creates bubbles by lowering thesolubility of gases (includingwater andCO2) that are dissolved in the lava, causing the gases to rapidlyexsolve (like the bubbles of CO2 that appear when a carbonated drink is opened). The simultaneous cooling and depressurization freeze the bubbles in amatrix. Pumice is fragments of lava ortephra that cooled in air or water. If pumice from an underwater volcanic eruption reaches the water surface, it can form pumice rafts on the water surface that can be a hazard for ships.[3]
Pumice is composed of highlymicrovesicularvolcanic glass with very thin, translucent bubble walls of pyroclastic igneous rock. It is commonly[4] but not exclusively ofsilicic orfelsic to intermediate in composition (e.g.,rhyolitic,dacitic,andesite,pantellerite,phonolite,trachyte). Pumice is commonly pale in color, ranging from white, cream, blue or grey, to green-brown or black. It forms whenvolcanic gases exsolving from viscousmagma form bubbles that remain within the viscous magma as it cools to glass. Pumice is a common product of explosive eruptions (plinian andignimbrite-forming) and commonly forms zones in upper parts of siliciclavas. Pumice has aporosity of 64–85% by volume and it floats on water, possibly for years, until it eventually becomes waterlogged and sinks.[5][6] As an example, trachytic pumice from the 2021 eruption ofFukutoku-Okanoba (a submarine volcano) has a porosity ranging from 73% to 91%, with an average of 78% for floating samples and 75% for submerged samples.[7]
There are two main forms of vesicle. Most pumice contains tubular microvesicles that can impart a silky or fibrous fabric. The elongation of the microvesicles occurs due toductile elongation in the volcanic conduit or, in the case of pumiceous lavas, during flow. The other form of vesicles are subspherical to spherical and result from highvapor pressure during an eruption.[8]
Pumice is considered avolcanic glass because it typically lacks a propercrystal structure. It can have no phenocrysts and/or microlites. The white pumices erupted by Pinatubo in 1991 are examples of pumice with an unusually high phenocryst content. Pumice varies in density according to the thickness of the solid material between the bubbles; many samples float in water. After the explosion ofKrakatoa,pumice rafts drifted through the Indian Ocean for up to 20 years, with tree trunks floating among them.[9] In fact, pumice rafts disperse and support several marine species.[10] In 1979, 1984 and 2006, underwater volcanic eruptions nearTonga created large pumice rafts that floated hundreds of kilometres toFiji.[11]
When larger amounts of gas are present, the result is a finer-grained variety of pumice known aspumicite. Pumicite consists of particles less than 4 mm (0.16 in) in size.[12][contradictory] Pumicite isash-sized particles of pumice[contradictory] and usually forms inPlinian eruptions or other eruptions with unusually high magma fragmentation.
Scoria differs from pumice in being denser. With larger vesicles and thicker vesicle walls, scoria sinks rapidly. The difference is the result of the lower viscosity of the magma that forms scoria.
Reticulite is a type ofmafic pumice that originates from unusually talllava fountains (at least 300 m (980 ft) high).[13] It extremely vesiculated variety of pumice consisting of a fragmented network of glass threads which join a series of points forming a polyhedral structure. It is formed by the collapse of the walls of the adjacent vesicles and the retraction of the fluid into threads which form the perimeters of the former polygonal faces. The threads are usually of triangular cross section, indicating chilling, before rounding could even take place. A synonym of it is thread-lace scoria even though it is not a true scoria.[14]
Illustrates the porous nature in detail.
Rocks from theBishop Tuff, uncompressed with pumice on left; compressed withfiamme on right
Two layers of pumice, first major phase of the Late-Bronze-Age volcano eruption (~1500 BC), southern part of thecaldera island Thera/Santorini. The lower layer is finer, almost white and without intrusions.
Pumice is an igneous rock with a foamy appearance. The name is derived from the Latin wordpumex (meaning "pumice")[15] which is related to the Latin wordspuma meaning "foam".[16] In former times, pumice was calledspuma maris, meaning "froth of the sea" in Latin because the frothy material was thought to be hardenedsea foam. Around 80 B.C., it was calledlapis 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.[17]
Pumice can be found all around the globe deriving from continental volcanic occurrences and submarine volcanic occurrences. Floating stones can also be distributed by ocean currents.[18] 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 tons 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.[19]
There are large reserves of pumice in Asian countries, for example Afghanistan, Indonesia, Japan, Syria, Iran, the Philippines and eastern Russia.
Considerable amounts of pumice can be found at theKamchatka Peninsula on the eastern flank of Russia. This area contains 19 active volcanoes and it lies in close proximity with thePacific volcanic belt.
Asia is also the site of the second-largest volcanic eruption in the 20th century, the1991 eruption of Mount Pinatubo, in the Philippines. Ash and pumicelapilli were distributed over a mile around the volcano. The June 15 eruption deposited two main types ofanhydrite-bearing pumice: a dominant porphyritic, phenocryst-rich white pumice and a subordinate phenocryst-poor gray/tan pumice.[20] These ejections filled trenches that once reached 200 m (660 ft) deep. So much magma was displaced from the vent that the volcano became a depression on the surface of the Earth.[21]
A basaltic trachyandesitic totrachydacitic pumice deposit underliesManila and is called the Diliman Tuff. It consists of anignimbrite along with reworked and airfall pumiceoustuff units. It is part of the larger Guadalupe Tuff Formation and is the youngest layer of it.Magma mixing and mingling is shown by banded textures in some of the pumice fragments, considerable range in groundmass composition (54 to 65 wt.% SiO2) in a single pumice fragment. The source volcano of this deposit has not yet been discovered. It is chemically distinct from adjacentTaal Caldera andLaguna Caldera with respect to both major- and trace-element concentrations.[22]
TheTaal Volcano south of Manila has also produced several extensive ignimbrite forming eruptions. The earliest of this unit is dated to 670ka and is called the Sampaga Formation.
Another well-known volcano that has produced pumice isKrakatoa. An eruption in 1883 ejected so much pumice that kilometers of sea were covered in floating pumice and in some areas the pumice raft thickness above sea level was 1.5 meters.[23]
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 theAeolian Islands of Italy, the island ofLipari 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 LatePleistocene (Tyrrhenian) to the Holocene.[24]
Pumice can be found all across North America including on theCaribbean Islands. In the United States, pumice is mined inNevada,Oregon,Idaho,Arizona,California,New Mexico andKansas. U.S. production of pumice and pumicite in 2011 was estimated at 380,000 tonnes, valued at $7.7 million with approximately 46% coming from Nevada and Oregon.[19] Idaho is also known as a large producer of pumice because of the quality and brightness of the rock found in local reserves.[25]
Mount Mazama in Oregon erupted 7,700 years ago and deposited 91 m (300 ft) of pumice and ash around the vent. The large amount of magma that was erupted caused the structure to collapse, forming a caldera now known asCrater Lake.[21]
Mount St. Helens produced a large amount of dacitic pumice in 1980. Two main types were observed which are the white/tan and gray types. The white type has phenocrysts while being little or absent in microlite content unlike the gray type which has the presence of microlites. Vesicularity for the white pumice is higher with around 85.7% vesicularity and thus is less dense while the gray type is lower with around 72.2% vesicularity and has a higher density. The vesicles of the white pumice are larger and more interconnected while the vesicles of the gray pumice are smaller, with hindered expansion and coalescence.[26]
Chile is one of the leading producers of pumice in the world.[27] ThePuyehue-Cordón Caulle are two coalesced volcanoes in theAndes mountains that ejected ash and pumice across Chile andArgentina. A recent eruption in 2011 wreaked havoc on the region by covering all surfaces and lakes in ash and pumice.[28]
TheHavre Seamount volcano produced the largest-known deep ocean volcanic eruption on Earth. The volcanoerupted in July 2012 but remained unnoticed until enormous pieces of pumice were seen to be floating on the Pacific Ocean. Blankets of rock reached a thickness of 5 meters.[29] Most of this floating pumice is deposited on the northwest coast ofNew Zealand and thePolynesia islands.
Themining 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.[30]
The detailed study of pumice, both in its areal andstratigraphic distribution, as well as in its internal structure and chemistry, plays an important role involcanology and the broaderEarth sciences. Several different types of internal structures and components in pumice exist at different scales and each allowsvolcanologists to decode different types of information about theeruption that formed the pumice. Beginning at the largest scale, pumice often contains abundantvesicles—void spaces left behind by bubbles that developed in the material while it was still molten, as a result of its formation byexplosive volcanism with abundantgas. The abundance and morphology of vesicles in pumice offer direct evidence ofvolatileexsolution anddegassing dynamics during the eruption that formed the rock. By analyzing vesicle size distributions, connectivity, and spatial arrangements, volcanologists can infer the history, style, andflow dynamics of a particular eruption. For instance, a high density of isolated vesicles may indicate rapiddecompression and limited bubble coalescence, characteristic of more explosive eruptions, while interconnected vesicle networks could suggest more efficient gas escape and a moreeffusive eruptive style.[31]
While vesicles in pumice constitute their own utility to volcano science, theglassymatrix or groundmass that makes up the larger part of the solid component in pumice can also provide a wealth of information for study. This matrix material consists of abundant, microscopic fragments of glass—quenched melt—representing the final bulk composition of themagma at the moment of eruption andfragmentation, and as such can be a kind ofgeochemical fingerprint, allowing researchers to identify the source of an eruption and reconstruct theevolution of its magma. Additionally, the distribution and composition ofcrystals andlithic fragments embedded in the pumice matrix provide a window into the history of magmatic processes in the subsurface. Careful analysis of the mineral assemblages in pumice can be used to determine temperature, pressure, and volatile content in themagma chamber and greatertranscrustal volcanic plumbing system. Volcanologists can examine the distribution of crystal sizes in pumice and usediffusion chronometry to examine compositional zoning in individual crystals in order to gain an understanding into the timescales involved in a single eruption—theresidence time of the crystal in the magma chamber before it was erupted.[32] Lithic fragments, derived from the walls of volcanic conduits or from thecountry rock, offer additional evidence in the way of eruptive processes andwall-rock assimilation.[33]
Finally, at the smallest scale,melt inclusions trapped within growing crystals in the melt and preserved in the erupted pumice product serve as time capsules of magmatic conditions prior to and during eruption. These inclusions may contain a variety of materials ranging fromsilicatemelt, volatiles such as H2O and CO2, and less frequently,sulfides and/orhalogens, preserving information about the pre-eruptive volatile budget andredox state of the magma chamber. Analysis of the shapes of melt inclusions—namely, the degree to which originally bubble-shaped melt inclusions have become faceted over time—can be used as an additionalchronometer and indication of magma residence time and repose of the volcanic system. Through detailed analysis of melt inclusion chemistry and volatile contents, volcanologists can reconstruct the conditions of a volcanic system in the subsurface prior to eruption, providing information about the eruptive process that not only increases understanding of volcanic eruptions as a subject of scientific study, but also helps scientists and policymakers in the area of planning forvolcanic hazards. As such, pumice is not merely a product of explosive volcanism, but a vital archive of eruptive processes and magmatic evolution.[34][35]
Pumice is a very lightweight, porous and abrasive material and it has been used for centuries in the construction and beauty industries as well as in early medicine. It is also used as anabrasive, especially inpolishes, pencilerasers, and the production ofstone-washedjeans. Pumice was also used in the early book-making industry to prepare parchment paper and leather bindings.[36] There is high demand for pumice, particularly for water filtration, chemical spill containment, cement manufacturing,[37] 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 theThree Sisters Wilderness.[38]
Pumice has been used in the medicinal industry for more than 2000 years. Ancient Chinese medicine used ground pumice along with groundmica and fossilized bones added to teas to calm the spirit. This tea was used to treat dizziness, nausea, insomnia, and anxiety disorders. Ingestion of these pulverized rocks was believed to be able to soften nodules and was later used with other herbal ingredients to treat gallbladder cancer and urinary difficulties. In Western medicine, beginning in the early 18th century, pumice ground into a sugar consistency mixed with other ingredients was used to attempt to treat ulcers mostly on the skin and cornea. Concoctions such as these were also used to help wounds scar in a supposedly healthier manner. In approximately 1680 it was noted by an English naturalist that pumice powder was used to promote sneezing.[39]
Pumice has been used as a material in personal care for thousands of years. It is an abrasive material that can be used in powdered form or as a stone to remove unwanted hair or skin. In ancientEgypt, it was common to remove all hair on the body to controllice and as a form of ritual purification, using creams, razors, and pumice stones.[40] Pumice in powdered form was an ingredient in toothpastes in ancient Rome.[41] Nail care was very important in ancient China; nails were kept groomed with pumice stones, and pumice stones were also used to remove calluses.
It was discovered in a Roman poem that pumice was used to remove dead skin as far back as 100 BC, and likely before then.[42] It has been used throughout many eras since then, including theVictorian era. Today, many of these techniques are still used; pumice is widely used as a skinexfoliant. Even though hair removal techniques have evolved over the centuries, abrasive material like pumice stones is also still used. "Pumice stones" are often used in beauty salons during thepedicure process to remove dry and excess skin from the bottom of the foot as well ascalluses.
Finely ground pumice has been added to sometoothpastes as a polish, similar to Roman use, and easily removesdental plaque build-up. Such toothpaste is too abrasive for daily use. Pumice is also added to heavy-duty hand cleaners (such aslava soap) as a mild abrasive. Some brands ofchinchilladust bath are formulated with powdered pumice. Old beauty techniques using pumice are still employed today but newer substitutes are easier to obtain.
Pumice stone, sometimes attached to a handle,[43] is an effective scrubbing tool for removal of limescale, rust, hard water rings, and other stains on porcelain fixtures in households (e.g., bathrooms). It is a quick method compared to alternatives like chemicals orvinegar andbaking soda orborax.
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 ofcarbon dioxide andoxygen 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 occur.
Another benefit of this inorganic rock is that it does not attract or hostfungi orinsects. As drainage is very important in horticulture, with the presence of pumicetillage is much easier. Pumice usage also creates ideal conditions for growing plants likecacti andsucculents as it increases the water retention in sandy soils and reduces the density ofclayey soils to allow more transportation of gases and water. The addition of pumice to soil improves and increases vegetative cover as the roots of plants make slopes more stable therefore it helps reduceerosion. 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. Chemically pumice ispH neutral, neitheracidic noralkaline.[44] In 2011, 16% of pumice mined in the United States was used for horticultural purposes.[19]
Pumice contributes to soil fertility in areas where it is naturally present in the soil due to volcanic activity. For example, in theJemez Mountains of New Mexico, theAncestral Puebloans settled on "pumice patches" of theEl Cajete Pumice which likely retained a greater amount of moisture and was ideal for farming.[45]
Pumice is widely used to make lightweightconcrete andinsulative low-densitycinder blocks. The air-filled vesicles in this porous rock serve as a good insulator.[21] A fine-grained version of pumice calledpozzolan is used as an additive in cement and is mixed withlime to form a light-weight, smooth, plaster-like concrete. This form of concrete was used as far back asRoman times. Roman engineers utilized it to build the huge dome of thePantheon with increasing amounts of pumice added to concrete for higher elevations of the structure. It was also commonly used as a construction material for manyaqueducts.
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.[46]
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 greenhouse gas emissions and fossil fuel consumption.[37]
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