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Diatomaceous earth (), diatomite (), or kieselgur/kieselguhr is a naturally occurring, soft, siliceous
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 
μm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of Uni ...
to less than 1  mm, but typically 10 to 200 μm. Depending on the granularity, this powder can have an abrasive feel, similar to
pumice 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 v ...
powder, and has a low
density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...
as a result of its high
porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measur ...
. The typical chemical composition of oven-dried diatomaceous earth is 80–90%
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
, with 2–4% alumina (attributed mostly to clay minerals), and 0.5–2% iron oxide. Diatomaceous earth consists of the
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
ized remains of diatoms, a type of hard-shelled microalgae. It is used as a filtration aid, mild abrasive in products including metal polishes and toothpaste, mechanical insecticide, absorbent for liquids, matting agent for coatings, reinforcing filler in plastics and rubber, anti-block in plastic films, porous support for chemical catalysts, cat litter, activator in
coagulation Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism ...
studies, a stabilizing component of dynamite, a thermal insulator, and a soil for potted plants and trees as in the art of
bonsai Bonsai ( ja, 盆栽, , tray planting, ) is the Japanese art of growing and training miniature trees in pots, developed from the traditional Chinese art form of '' penjing''. Unlike ''penjing'', which utilizes traditional techniques to produc ...
.


Composition

Each deposit of diatomaceous earth is different, with varying blends of pure diatomaceous earth combined with other natural clays and minerals. The diatoms in each deposit contain different amounts of silica, depending on the sedimentation conditions, on the presence of other sediments (clay, sand, volcanic ashes), and on the age of the deposit ( diagenesis,
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
(SiO2) dissolution/precipitation, diatoms tests ageing). The species of diatom may also differ among deposits. The species of diatom is dependent upon the age and paleoecology of the deposit. In turn, the shape of a diatom is determined by its species. Many deposits throughout
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, for ...
, such as Red Lake Earth, are from the
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
epoch and contain a species of diatom known as ''Melosira granulata''. These diatoms are approximately 12 to 13 million years old and have a small globular shape. A deposit containing diatoms from this epoch can provide certain benefits over others. For example, diatoms from the
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...
epoch (approximately 40 to 50 million years old) are not as effective in their ability to absorb fluids because as older diatoms recrystallize, their small pores become filled with silica.


Formation

Diatomite forms by the accumulation of the amorphous silica (
opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...
, ) remains of dead diatoms (microscopic single-celled algae) in
lake sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand a ...
or marine sediments. The
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
remains consist of a pair of symmetrical shells or frustules. Marine diatomites are found in association with a wide variety of other rock types but lacustrine diatomites are almost always associated with volcanic rock. Diatomaceous
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...
consists of diatomite that has been cemented with silica. Diatoms are able to extract silica from water that is less than 1% saturated in amorphous silica (saturation index (SI): -2). Their frustules remain undissolved because they are surrounded by an organic matrix. Clay minerals may also precipitate on the frustules and protect them from dissolution in sea water. When the diatom dies, the frustule is stripped of its organic layer and exposed to sea water. As a result, only 1% to 10% of frustules survive long enough to be buried under sediments and some of this is dissolved within the sediments. Only an estimated 0.05% to 0.15% of the original amount of silica produced by diatoms is preserved in the sedimentary record.


Discovery

In 1836 or 1837, German peasant Peter Kasten discovered diatomaceous earth (German: ''Kieselgur'') when sinking a well on the northern slopes of the Haußelberg hill, in the Lüneburg Heath in North Germany. The extraction site on the Lüneburg Heath was 1863–1994 Neuohe, while the storage sites were: The deposits are up to thick and are all of freshwater diatomaceous earth. File:KieselgurNeuohe4-2.jpg, c. 1900–1910 Diatomaceous earth pit at Neuohe File:KieselgurNeuohe3-2.jpg, c. 1900–1910 a drying area: one firing pile is being prepared; another is under way File:KieselgurNeuohe2-2.jpg, 1913: Staff at the Neuohe factory, with male workers and a female cook in front of a drying shed Until
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
, almost the entire worldwide production of diatomaceous earth was from this region.


Other deposits

In Poland diatomaceous earth deposits are found in Jawornik, and are composed mostly of diatomaceous skeletons (frustules) In Germany, diatomaceous earth was also extracted at Altenschlirf on the Vogelsberg ( Upper Hesse) and at
Klieken Klieken is a village and a former municipality in the district of Wittenberg, Saxony-Anhalt Saxony-Anhalt (german: Sachsen-Anhalt ; nds, Sassen-Anholt) is a state of Germany, bordering the states of Brandenburg, Saxony, Thuringia and Lo ...
(
Saxony-Anhalt Saxony-Anhalt (german: Sachsen-Anhalt ; nds, Sassen-Anholt) is a state of Germany, bordering the states of Brandenburg, Saxony, Thuringia and Lower Saxony. It covers an area of and has a population of 2.18 million inhabitants, making i ...
). There is a layer of diatomaceous earth more than thick in the nature reserve of Soos in the Czech Republic. Deposits on the Isle of Skye, off the west coast of Scotland, were mined until 1960. In
Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the ...
and in Clark County, Nevada, United States, there are deposits that are up to several hundred meters thick in places. Marine deposits have been worked in the Sisquoc Formation in Santa Barbara County, California near Lompoc and along the
Southern California Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban ...
coast The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
. This is the world's largest deposit of diatomite. Additional marine deposits have been worked in
Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean t ...
,
Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth are ...
,
Algeria ) , image_map = Algeria (centered orthographic projection).svg , map_caption = , image_map2 = , capital = Algiers , coordinates = , largest_city = capital , relig ...
and the MoClay of Denmark. Freshwater lake deposits occur in Nevada,
Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
,
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...
and
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
. Lake deposits also occur in interglacial lakes in the eastern United States, in Canada and in Europe in Germany, France, Denmark and the Czech Republic. The worldwide association of diatomite deposits and
volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...
deposits suggests that the availability of silica from
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...
may be necessary for thick diatomite deposits. Diatomaceous earth is sometimes found on desert surfaces. Research has shown that the erosion of diatomaceous earth in such areas (such as the Bodélé Depression in the Sahara) is one of the most important sources of climate-affecting dust in the atmosphere. The siliceous frustules of diatoms accumulate in fresh and brackish wetlands and lakes. Some peats and mucks contain a sufficient abundance of frustules such that they can be mined. Most of Florida's diatomaceous earths have been found in the muck of wetlands or lakes. The American Diatomite Corporation, from 1935 to 1946, refined a maximum of 145 tons per year from their processing plant near Clermont, Florida. Muck from several locations in Lake County, Florida was dried and burned ( calcined) to produce the diatomaceous earth. It was formerly extracted from Lake Mývatn in Iceland. The commercial deposits of diatomite are restricted to
Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...
or Quaternary periods. Older deposits from as early as the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
Period are known, but are of low quality.Cummins, Arthur B., ''Diatomite'', in ''Industrial Minerals and Rocks'', 3rd ed. 1960, American Institute of Mining, Metallurgical, and Petroleum Engineers, pp. 303–319 Diatomite deposits rich in fossils have been located in New Zealand, but mining of the Foulden Maar deposits on an industrial scale, for conversion to animal feed, has drawn strong opposition.


Commercial form

Diatomaceous earth is available commercially in several formats: *
granulated Granulation is the process of forming grains or granules from a powdery or solid substance, producing a granular material. It is applied in several technological processes in the chemical and pharmaceutical industries. Typically, granulation invo ...
diatomaceous earth is a raw material simply crushed for convenient packaging * milled or micronized diatomaceous earth is especially fine (10 μm to 50 μm) and used for insecticides. * calcined diatomaceous earth is heat-treated and activated for filters.


Usages


Explosives

In 1866, Alfred Nobel discovered that nitroglycerin could be made much more stable if absorbed in diatomite (kieselguhr). This allowed a much safer transport and handling than pure nitroglycerin under the liquid form. Nobel patented this mixture as dynamite in 1867; the mixture is also called guhr dynamite by reference to the German term kieselguhr.


Filtration

The Celle engineer, Wilhelm Berkefeld, recognized the ability of the diatomaceous earth to filter and developed tubular filters (known as filter candles) fired from diatomaceous earth. During the cholera
epidemic An epidemic (from Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of patients among a given population within an area in a short period of time. Epidemics of infectious ...
in
Hamburg Hamburg (, ; nds, label=Hamburg German, Low Saxon, Hamborg ), officially the Free and Hanseatic City of Hamburg (german: Freie und Hansestadt Hamburg; nds, label=Low Saxon, Friee un Hansestadt Hamborg),. is the List of cities in Germany by popul ...
in 1892, these
Berkefeld filter A Berkefeld filter is a water filter made of diatomaceous earth (''Kieselguhr''). It was invented in Germany in 1891, and by 1922 was being marketed in the United Kingdom by the Berkefeld Filter Co. Berkefeld was the name of the owner of the ...
s were used successfully. One form of diatomaceous earth is used as a filter medium, especially for swimming pools. It has a high porosity because it is composed of microscopically small, hollow particles. Diatomaceous earth (sometimes referred to by trademarked brand names such as Celite) is used in chemistry as a filtration aid, to increase flow rate, and filter very fine particles that would otherwise pass through or clog filter paper. It is also used to filter water, particularly in the drinking water treatment process and in fish tanks, and other liquids, such as beer and wine. It can also filter syrups, sugar, and honey without removing or altering their color, taste, or nutritional properties.


Abrasive

The oldest use of diatomite is as a very mild abrasive and has been used in toothpaste, metal polishes, and some facial scrubs.


Pest control

Diatomite is of value as an insecticide because of its abrasive and physico- sorptive properties. The fine powder adsorbs
lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids in ...
s from the waxy outer layer of the
exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton ( endoskeleton) in for example, a human. In usage, some of the ...
s of many species of insects; this layer acts as a barrier that resists the loss of water vapour from the insect's body. Damaging the layer increases the evaporation of water from their bodies, so that they dehydrate, often fatally.
Arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s die as a result of the water pressure deficiency, based on Fick's laws of diffusion. This also works against gastropods and is commonly employed in gardening to defeat slugs. However, since slugs inhabit humid environments, efficacy is very low. Diatomaceous earth is sometimes mixed with an attractant or other additives to increase its effectiveness. The shape of the diatoms contained in a deposit has not been proven to affect their functionality when it comes to the adsorption of lipids; however, certain applications, such as that for slugs and snails, do work best when a particularly shaped diatom is used, suggesting that lipid adsorption is not the whole story. For example, in the case of slugs and snails, large, spiny diatoms work best to lacerate the epithelium of the mollusk. Diatom shells will work to some degree on the vast majority of animals that undergo ecdysis in shedding cuticle, such as
arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s or nematodes. It also may have other effects on
lophotrochozoa Lophotrochozoa (, "crest/wheel animals") is a clade of protostome animals within the Spiralia. The taxon was established as a monophyletic group based on molecular evidence. The clade includes animals like annelids, molluscs, bryozoans, bra ...
ns, such as
mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is e ...
s or annelids. Medical-grade diatomite has been studied for its efficacy as a
deworming Deworming (sometimes known as worming, drenching or dehelmintization) is the giving of an anthelmintic drug (a wormer, dewormer, or drench) to a human or animals to rid them of helminths parasites, such as roundworm, flukes and tapeworm. Pur ...
agent in cattle; in both studies cited the groups being treated with diatomaceous earth did not fare any better than control groups. It is commonly used in lieu of boric acid and can be used to help control and possibly eliminate
bed bugs Bed bugs are insects from the genus ''Cimex'' that feed on blood, usually at night. Their bites can result in a number of health impacts including skin rashes, psychological effects, and allergic symptoms. Bed bug bites may lead to skin changes ...
, house dust mite,
cockroach Cockroaches (or roaches) are a paraphyletic group of insects belonging to Blattodea, containing all members of the group except termites. About 30 cockroach species out of 4,600 are associated with human habitats. Some species are well-known ...
, ant, and
flea Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, ...
infestations. Diatomaceous earth is widely applied for insect control in grain storage. In order to be effective as an insecticide, diatomaceous earth must be uncalcinated (i.e., it must not be heat-treated prior to application) and have a mean particle size below about 12 μm (i.e., food grade— see below). Although considered to be relatively low-risk, pesticides containing diatomaceous earth are not exempt from regulation in the United States under the Federal Insecticide, Fungicide, and Rodenticide Act and must be registered with the Environmental Protection Agency.


Thermal

Its thermal properties enable it to be used as the barrier material in some fire-resistant safes. It is also used in evacuated powder insulation for use with cryogenics. Diatomaceous earth powder is inserted into the vacuum space to aid in the effectiveness of vacuum insulation. It was used in the classical AGA cookers as a thermal heat barrier.


Catalyst support

Diatomaceous earth also finds some use as a
support Support may refer to: Arts, entertainment, and media * Supporting character Business and finance * Support (technical analysis) * Child support * Customer support * Income Support Construction * Support (structure), or lateral support, a ...
for
catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s, generally serving to maximize a catalyst's
surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of ...
and activity. For example,
nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...
can be supported on the material—the combination is called Ni–Kieselguhr—to improve its activity as a
hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...
catalyst.


Agriculture

Natural freshwater diatomaceous earth is used in agriculture for grain storage as an anticaking agent, as well as an insecticide. It is approved by the Food and Drug Administration as a feed additive to prevent caking. Some believe it may be used as a natural anthelmintic (dewormer), although studies have not shown it to be effective. Some farmers add it to their livestock and
poultry Poultry () are domesticated birds kept by humans for their eggs, their meat or their feathers. These birds are most typically members of the superorder Galloanserae (fowl), especially the order Galliformes (which includes chickens, qu ...
feed to prevent the caking of feed. "Food-Grade Diatomaceous Earth" is widely available in agricultural feed supply stores. Freshwater diatomite can be used as a growing medium in hydroponic gardens. It is also used as a growing medium in potted plants, particularly as
bonsai Bonsai ( ja, 盆栽, , tray planting, ) is the Japanese art of growing and training miniature trees in pots, developed from the traditional Chinese art form of '' penjing''. Unlike ''penjing'', which utilizes traditional techniques to produc ...
soil. Bonsai enthusiasts use it as a soil additive, or pot a bonsai tree in 100% diatomaceous earth. In vegetable gardening it is sometimes used as a soil conditioner, because like perlite, vermiculite, and expanded clay, it retains water and nutrients, while draining fast and freely, allowing high oxygen circulation within the growing medium.


Marker in livestock nutrition experiments

Natural dried, not calcinated diatomaceous earth is regularly used in livestock nutrition research as a source of acid-insoluble ash (AIA), which is used as an indigestible marker. By measuring the content of AIA relative to nutrients in test diets and feces or digesta sampled from the terminal ileum (last third of the small intestine) the percentage of that nutrient digested can be calculated using the following equation: where: Natural freshwater diatomaceous earth is preferred by many researchers over chromic oxide, which has been widely used for the same purpose, the latter being a known carcinogen and, therefore, a potential hazard to research personnel.


Construction

Spent diatomaceous earth from the brewing process can be added to ceramic mass for the production of red bricks with higher open porosity. Diatomaceous earth is considered a very prominent inorganic non-metallic material that can be utilized for the production of various ceramics, including production of porous ceramics under low temperature hydrothermal technology.


Specific varieties

* Tripolite is the variety found in
Tripoli, Libya Tripoli (; ar, طرابلس الغرب, translit= Ṭarābulus al-Gharb , translation=Western Tripoli) is the capital and largest city of Libya, with a population of about 1.1 million people in 2019. It is located in the northwest of Libya o ...
. * Bann clay is the variety found in the Lower Bann valley in Northern Ireland. * ''Moler'' ( mo-clay) is the variety found in northwestern Denmark, especially on the islands of Fur and Mors. * ''Freshwater-derived food grade'' diatomaceous earth is the type used in United States agriculture for grain storage, as feed supplement, and as an insecticide. It is produced uncalcinated, has a very fine particle size, and is very low in crystal silica (<2%). * ''Salt-water-derived pool / beer / wine filter grade'' is not suitable for human consumption or effective as an insecticide. Usually calcinated before being sold to remove impurities and undesirable volatile contents, it is composed of larger particles than the freshwater version and has a high crystalline silica content (>60%).


Microbial degradation

Certain species of bacteria in oceans and lakes can accelerate the rate of dissolution of silica in dead and living diatoms by using
hydrolytic Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis i ...
enzymes to break down the organic algal material.


Climatologic importance

The Earth's
climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...
is affected by
dust Dust is made of fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian process), volcanic eruptions, and pollution. Dust in ...
in the atmosphere, so locating major sources of atmospheric dust is important for
climatology Climatology (from Greek , ''klima'', "place, zone"; and , '' -logia'') or climate science is the scientific study of Earth's climate, typically defined as weather conditions averaged over a period of at least 30 years. This modern field of stu ...
. Recent research indicates that surface deposits of diatomaceous earth play an important role. Research shows that significant dust comes from the Bodélé Depression in
Chad Chad (; ar, تشاد , ; french: Tchad, ), officially the Republic of Chad, '; ) is a landlocked country at the crossroads of North and Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic ...
, where storms push diatomite gravel over dunes, generating dust by abrasion.


Safety considerations

Inhalation of ''crystalline'' silica is harmful to the lungs, causing silicosis. ''Amorphous'' silica is considered to have low toxicity, but prolonged inhalation causes changes to the lungs. Diatomaceous earth is mostly amorphous silica but contains some crystalline silica, especially in the saltwater forms. In a 1978 study of workers, those exposed to natural diatomaceous earth for over five years had no significant lung changes while 40% of those exposed to the calcined form had developed pneumoconiosis. Today's common diatomaceous earth formulations are safer to use, as they are predominantly made up of amorphous silica and contain little or no crystalline silica. The crystalline silica content of diatomaceous earth is regulated in the United States by the
Occupational Safety and Health Administration The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agen ...
(OSHA) and there are guidelines from the National Institute for Occupational Safety and Health that set maximum amounts allowable in the product (1%) and in the air near the breathing zone of workers, with a recommended exposure limit at 6 mg/m3 over an 8-hour workday. OSHA has set a
permissible exposure limit The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agent such as high level noise. Permissible exposure limits are established by the Occupationa ...
for diatomaceous earth as 20 mppcf (80 mg/m3/%SiO2). At levels of 3,000 mg/m3, diatomaceous earth is immediately dangerous to life and health. In the 1930s, long-term occupational exposure among workers in the cristobalite diatomaceous earth industry who were exposed to high levels of airborne crystalline silica over decades were found to have an increased risk of silicosis. Today, workers are required to use respiratory-protection measures when concentrations of silica exceed allowable levels. Diatomite produced for pool filters is treated with high heat (
calcination Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), gen ...
) and a fluxing agent ( soda ash), causing the formerly harmless amorphous silicon dioxide to assume its crystalline form.


See also

* * * * * * *


References


Occupational exposure to crystalline silica and autoimmune disease.


External links

*


Diatomite: Statistics and Information – USGS


Citat: "...A diatomaceous earth consisting of opaline silica..."

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