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| [[File:Diatomaceous Earth.jpg|right|thumb|300px|A sample of food-grade diatomaceous earth]]
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| '''Diatomaceous earth''' {{IPAc-en|ˌ|d|aɪ|.|ə|t|ə|ˌ|m|eɪ|ʃ|ə|s|_|ˈ|ɜr|θ}} also known as '''D.E.''', '''diatomite''', or '''kieselgur'''/'''kieselguhr''', is a naturally occurring, soft, [[siliceous]] [[sedimentary rock]] that is easily crumbled into a fine white to off-white powder. It has a particle size ranging from less than 3 [[micrometres]] to more than 1 millimeter, but typically 10 to 200 micrometres. Depending on the granularity, this powder can have an [[abrasive]] feel, similar to [[pumice]] powder, and is very light as a result of its high [[porosity]]. The typical chemical composition of oven-dried diatomaceous earth is 80 to 90% [[silica]], with 2 to 4% [[alumina]] (attributed mostly to [[clay mineral]]s) and 0.5 to 2% [[iron oxide]].<ref name="USGS">{{cite book |last=Antonides |first=Lloyd E. |title=Diatomite |year=1997 |publisher=[[U.S.G.S.]] |url=http://minerals.usgs.gov/minerals/pubs/commodity/diatomite/250497.pdf |accessdate=2010-12-12 |format=PDF}}</ref>
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| Diatomaceous earth consists of fossilized remains of [[diatom]]s, a type of hard-shelled [[algae]]. It is used as a [[filtration]] aid, mild abrasive in products including [[toothpaste]], mechanical [[insecticide]], [[absorption (chemistry)|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 [[blood clotting]] studies, a stabilizing component of [[dynamite]], and a [[thermal insulation|thermal insulator]].
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| == Geology and occurrence ==
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| [[File:Diatomaceous Earth BrightField.jpg|thumb|right|300px|Diatomaceous earth as viewed under [[bright field microscopy|bright field]] illumination on a [[light microscope]]. Diatomaceous earth is made up of the [[cell walls]]/[[exoskeleton|shells]] of single cell [[diatoms]] and readily crumbles to a fine powder. Diatom cell walls are made up of biogenic [[silica]]; silica synthesised in the diatom cell by the [[polymerisation]] of [[silicic acid]]. This image of diatomaceous earth particles in water is at a scale of 6.236 pixels/[[μm]], the entire image covers a region of approximately 1.13 by 0.69 mm.]]
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| === Formation ===
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| Diatomite forms by the accumulation of the [[amorphous]] silica ([[opal]], SiO<sub>2</sub>·nH<sub>2</sub>O) remains of dead diatoms (microscopic single-celled [[algae]]) in [[Lake|lacustrine]] or [[Marine (ocean)|marine]] [[sediment]]s. The [[fossil]] remains consist of a pair of symmetrical shells or [[frustules]].<ref name="USGS" />
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| === Discovery ===
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| In 1836 or 1837, the [[peasant]] and goods waggoner Peter Kasten<ref>http://www.bonsaitreestuff.com/diatomaceous-earth/ + Heinrich Küsel „Der Speicher“ v.1930 {{dead link|date=December 2010}}</ref> discovered diatomaceous earth (German: kieselgur) when sinking a well on the northern slopes of the [[Haußelberg]] hill, in the [[Lüneburg Heath]] in north [[Germany]]. Initially, it was thought that [[limestone]] had been found, which could be used as fertilizer. [[Alfred Nobel]] used the properties of diatomaceous earth in the manufacture of [[dynamite]]. The [[Celle]] engineer Wilhelm Berkefeld recognized its ability to filter, and developed tubular filters (known as filter candles) fired from diatomaceous earth.<ref>[http://www.elga-berkefeld.de/de/unternehmen/commitments/ ELGA Berkefeld Water Treatment] (Wasseraufbereitung){{dead link|date=July 2013}}</ref> During the [[cholera]] [[epidemic]] in [[Hamburg]] in 1892, these [[Berkefeld filter]]s were used successfully.
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| === Extraction and storage sites in the Lüneburg Heath ===
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| *Neuohe – extraction from 1863 to 1994
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| *Wiechel from 1871 to 1978
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| *Hützel from 1876 to 1969
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| *Hösseringen from ca. 1880 to 1894
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| *Hammerstorf from ca. 1880 to 1920
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| *Oberohe from 1884 to 1970
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| *Schmarbeck from 1896 to ca. 1925
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| *Steinbeck from 1897 to 1928
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| *Breloh from 1907 to 1975
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| *Schwindebeck from 1913 to 1975
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| *Hetendorf from 1970 to 1994
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| The [[Lagerstätten|deposits]] are up to {{convert|28|m|ft}} thick and are all of freshwater diatomaceous earth.
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| <gallery>
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| File:KieselgurNeuohe4-2.jpg|ca. 1900–1910 Diatomaceous earth pit at Neuohe
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| File:KieselgurNeuohe3-2.jpg|ca. 1900–1910 a drying area: one firing pile is being prepared; another is under way
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| File:KieselgurNeuohe2-2.jpg|1913 Staff at the Neuohe factory, with workers and a female cook in front of a drying shed
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| </gallery>
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| Until the [[First World War]] almost the entire worldwide production of diatomaceous earth was from this region.
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| === Other deposits ===
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| In Germany diatomaceous earth was also extracted at [[Altenschlirf]] <ref>http://www2.natpa.de/bonifatius/senken/p7.htm Über den früheren Abbau von Kieselgur im Vogelsberg/Hessen{{dead link|date=July 2013}}</ref> on the [[Vogelsberg]] ([[Upper Hesse]]) and at [[Klieken]] <ref>[http://homepages.compuserve.de/tmby100/kieselgur.htm Geschichte des Kieselgurabbaus in Klieken]{{dead link|date=July 2013}}</ref> ([[Saxony-Anhalt]]).
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| There is a layer of diatomaceous earth up to {{convert|4|m|ft}} thick in the nature reserve of [[Soos (Nature reservation)|Soos]] in the [[Czech Republic]].
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| In [[Colorado]] and in [[Clark County, Nevada]], United States, there are deposits that are up to several hundred metres thick in places. Marine deposits have been worked in the [[Sisquoc Formation]] in [[Santa Barbara County, California]] near [[Lompoc, California|Lompoc]] and along the [[Southern California]] [[coast]]. Additional marine deposits have been worked in [[Maryland]], [[Virginia]], [[Algeria]] and the [[MoClay]] of Denmark. Fresh water lake deposits occur in Nevada, [[Oregon]], [[Washington (U.S. state)|Washington]] and [[California]]. 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]] deposits suggests that the availability of silica from [[volcanic ash]] may be necessary for thick diatomite deposits.<ref name=AIME/>
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| Sometimes diatomaceous earth is found on the surface in [[desert]]s. 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.
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| The commercial deposits of diatomite are restricted to [[Tertiary]] or [[Quaternary]] periods. Older deposits from as early as the [[Cretaceous]] Period are known, but are of low quality.<ref name=AIME>Cummins, Arthur B., ''Diatomite'', in ''Industrial Minerals and Rocks'', 3rd ed. 1960, [[American Institute of Mining, Metallurgical, and Petroleum Engineers]], pp. 303–319</ref>
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| == Applications ==
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| === Industrial ===
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| [[File:Diatomaceous earth closeup 2001-10-18.jpg|thumb|right|Individual diatom cell walls often maintain their shape even in commercially processed filter media, such as this one for swimming pools]]
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| [[File:Diatoms through the microscope.jpg|thumb| Live marine diatoms from Antarctica (magnified)]]
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| In 1866, [[Alfred Nobel]] discovered that [[nitroglycerin]] could be made much more stable if absorbed in diatomite. This allows much safer transport and handling than nitroglycerin in its raw form. He patented this mixture as [[dynamite]] in 1867, and the mixture is also called guhr dynamite.
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| === Filtration ===
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| One form of diatomaceous earth is used as a [[filter (chemistry)|filter]] medium, especially for swimming pools. It has a high porosity, because it is composed of microscopically small, coffin-like, hollow particles. Diatomaceous earth (sometimes referred to by trademarked brand names such as Celite) is used in chemistry as a filtration aid, to 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 [[aquarium|fish tanks]], and other liquids, such as [[beer]] and [[wine]]. It can also filter [[syrup]]s, [[sugar]], and honey without removing or altering their color, taste, or nutritional properties.<ref>{{Cite journal|last=Root|first=A.I.|author=|authorlink=|coauthors=E.R. Root|author-separator=|editor=|editorn=|editorn-last=|editorn-first=|editor-link=|editorn-link=|others=|title=The ABC and xyz of bee culture|type=|url=http://books.google.com/?id=i0PoSYNEsh0C&pg=PA387&lpg=PA387&dq=diatomaceous+earth+%22does+not+remove%22#v=onepage&q=diatomaceous%20earth%20%22does%20not%20remove%22&f=false|archiveurl=|archivedate=|format=|accessdate=March 8, 2011|edition=|series=|volume=|date=March 1, 2005|origyear=|year=|month=|publisher=Kessinger Publishing|location=|language=|isbn=978-1-4326-2685-3|oclc=|doi=|doi_inactivedate=|bibcode=|id=|page=387|pages=|nopp=|at=|chapter=|chapterurl=|quote=|laysummary=|laydate=|separator=|postscript=<!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}|lastauthoramp=|ref=}}</ref>
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| === Abrasive ===
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| The oldest use of diatomite is as a very mild abrasive and, for this purpose, it has been used both in [[toothpaste]] and in metal [[Polishing|polishes]], as well as in some facial scrubs.
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| === Pest control ===
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| Diatomite is used as an [[insecticide]], due to its abrasive and physico-[[sorptivity|sorptive]] properties.<ref>{{cite conference|url= http://home.cc.umanitoba.ca/~fieldspg/fields/de-test-p.pdf |title= Standardized testing for diatomaceous earth |last1= Fields |first1= Paul |last2= Allen |first2= Sylvia |first3= Zlatko |last3= Korunic |first4= Alan |last4= McLaughlin |first5= Tanya |last5= Stathers |date= July 2002 |publisher= Entomological Society of Manitoba |booktitle= Proceedings of the Eighth International Working Conference of Stored-Product Protection |pages= |location= York, U.K. |id= }}</ref> The fine powder absorbs [[lipids]] from the waxy outer layer of insects' [[exoskeleton]]s, causing them to dehydrate.<ref>Staff. "Natural Methods for Controlling Fleas."http://www.xmission.com/~emailbox/fleas.htm</ref> [[Arthropod]]s die as a result of the water pressure deficiency, based on [[Fick's law of diffusion]]. This also works against [[gastropod]]s and is commonly employed in gardening to defeat [[slug]]s. However, since slugs inhabit humid environments, efficacy is very low. It is sometimes mixed with an attractant or other additives to increase its effectiveness. Medical-grade diatomite is sometimes used to [[De-worming|de-worm]] both animals and humans, with questionable efficacy.<ref>{{cite journal |last=Lartigue |first=E. del C. |last2=Rossanigo |first2=C. E. |year=2004 |title=Insecticide and anthelmintic assessment of diatomaceous earth in cattle |journal=Veterinaria Argentina |volume=21 |issue=209 |pages=660–674 |doi= }}</ref><ref>{{cite journal |last=Fernandez |first=M. I. |last2=Woodward |first2=B. W. |last3=Stromberg |first3=B. E. |year=1998 |title=Effect of diatomaceous earth as an anthelmintic treatment on internal parasites and feedlot performance of beef steers |journal=Animal Science |volume=66 |issue=3 |pages=635–641 |doi=10.1017/S1357729800009206 }}</ref> It is commonly used in lieu of [[boric acid]], and can be used to help control and possibly eliminate [[bed bug]], [[house dust mite]], [[cockroach]], [[ant]] and [[flea]] infestations.<ref name="Faulde">{{cite journal |first1=M. K. |last1=Faulde |first2=M. |last2=Tisch |first3=J. J. |last3=Scharninghausen |title=Efficacy of modified diatomaceous earth on different cockroach species (Orthoptera, Blattellidae) and silverfish (Thysanura, Lepismatidae) |journal=Journal of Pest Science |date=August 2006 |volume=79 |issue=3 |pages=155–161 |doi=10.1007/s10340-006-0127-8 |accessdate=2013-07-07}}</ref><ref>{{cite web |url=http://www.gardenharvestsupply.com/ProductCart/pc/Food-Grade-Diatomaceous-Earth-c11.htm |title=The Uses of Food Grade Diatomaceous Earth |publisher=gardenharvestsupply.com |date= |accessdate=2013-08-14}}</ref> This material has wide application for insect control in grain storage.<ref>{{cite web |url=http://www.survival-center.com/foodfaq/ff17-oxy.htm |title=The Food Storage Faq – Specific Specifications |publisher=Survival-center.com |date= |accessdate=2013-07-07}}</ref>
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| In order to be effective as an insecticide, diatomaceous earth must be [[calcination|uncalcinated]] (i.e., it must not be heat-treated prior to application)<ref>{{Cite book
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| |title=Encyclopedia of Entomology
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| |last=Capinera
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| |first=John L.
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| |authorlink=
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| |last2=
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| |first2=
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| |editor1-last=Capinera
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| |editor1-first=John L.
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| |edition=Second
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| |volume=
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| |year=2008
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| |origyear=
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| |page=1216
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| |chapter=Diatomaceous earth
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| |pages=
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| |publisher=Springer
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| |place=
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| |url=http://books.google.com/books?id=i9ITMiiohVQC&lpg=PA1216&dq=%22diatomaceous%20earth%22%20insecticide%20size&pg=PA1215#v=onepage&q=%22diatomaceous%20earth%22%20insecticide%20size&f=false
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| |accessdate=
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| |isbn=9781402062421
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| |oclc=
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| }}</ref> and have a mean particle size below about 12 µm (i.e., food-grade – see below).
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| 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]].<ref>{{cite web |url=http://www.epa.gov/pesticides/regulating/labels/labels_faq/lr_faq_1.html |title=Pesticide Labeling Questions & Answers | Pesticide Labeling Consistency | US EPA |publisher=[[United States Environmental Protection Agency|EPA]] |date=10 January 2013 |accessdate=2013-07-07}}</ref>
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| === Absorbent ===
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| Its absorbent qualities make it useful for spill clean-up and the U.S. [[Centers for Disease Control and Prevention]] recommends it to clean up [[toxic]] liquid spills. These qualities also lend themselves to use in facial masks to absorb excess oils.
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| It has been employed as a primary ingredient in a type of cat litter. The type of silica used in cat litter comes from freshwater sources and does not pose a significant health risk to pets or humans.
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| The microscopic matrix of diatomaceous earth make it a highly effective [[desiccant]]; it can absorb up to 1.1 times its weight in water.<ref>Laboratoir National d'Essais Dossier 9101133 – Document CEMATE/1 of December 1999</ref> It also can be used in the absorption of ethylene gas to reduce decay in fruits and produce.{{Citation needed|date=March 2013}} The combination of refrigeration and diatomaceous earth as a filter medium is one of the best ways to extend the shelf life of fruits and produce commercially and in a home refrigerator.{{Citation needed|date=March 2013}} One should use a food grade diatomaceous earth, as opposed to pool grade, when using it as a desiccant near fruit and produce.
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| === Thermal ===
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| Its thermal properties enable it to be used as the barrier material in some fire resistant safes. {{Citation needed|date=March 2013}} It is also used in evacuated powder insulation for use with cryogenics.<ref>Flynn, Thomas M. "Cryogenic Equipment and Cryogenic Systems Analysis." Cryogenic Engineering. Boca Raton [etc.: CRC, 2005. Print.</ref> 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.
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| === DNA purification ===
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| Diatomite (Celite) can be used for the removal of DNA in the presence of a highly concentrated [[chaotropic agent]] such as [[sodium iodide]], [[guanidine|guanidinium chloride]] and [[guanidinium thiocyanate]]. {{Citation needed|date=March 2013}} As with other silicates, the diatomites will remove double stranded DNA but not RNA or proteins. The DNA can be extracted from the diatomites using low ionic strength buffers, including water, at neutral to slightly alkaline pH. {{Citation needed|date=March 2013}} Crude diatomites of a uniform size must first be washed in a heated acid such as 5M [[hydrochloric acid|HCl]].<ref>{{cite journal |last=Goren |first=R. |last2=Baykara |first2=T. |last3=Marsoglu |first3=M. |title=A study on the purification of diatomite in hydrochloric acid |year=2002 |journal=Scand. J. of Metallurgy |volume=31 |issue=2 |pages=115–119 |doi=10.1034/j.1600-0692.2002.310205.x }}</ref> [[Calcination]] can further improve consistency of the material, while mild [[Corrosive substance|caustic]] treatment may improve adsorption with lower levels of chaotrophs. {{Citation needed|date=March 2013}}
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| === Use in agriculture ===
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| Natural freshwater diatomaceous earth is used in agriculture for grain storage as an [[anticaking agent]], as well as an insecticide.<ref>{{cite web |url=http://www.gov.mb.ca/agriculture/crops/cropproduction/faa06s00.html |title=Prevention and Management of Insects and Mites in Farm-Stored Grain |publisher=Province of Manitoba |date= |accessdate=2013-07-07}}</ref> It is approved by the United States Department of Agriculture as a feed supplement to prevent caking.<ref name="usdade" />
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| It is also used as a natural [[anthelmintic]] (dewormer). Some farmers add it to their livestock and [[Chicken|poultry]] feed to prevent the caking of feed.<ref name="usdade">[http://www.ars.usda.gov/is/np/mba/apr00/food.htm Diatomaceous Earth (DE)]{{dead link|date=July 2013}}</ref> "Food Grade Diatomaceous Earth" is widely available in agricultural feed supply stores. Diatomaceous earth is acceptable as an anti caking agent for livestock.<ref name="usdade" />
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| ==== Hydroponics ====
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| Freshwater diatomite can be used as a growing medium in [[hydroponic]] gardens.
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| It is also used as a growing medium in potted plants, particularly as [[bonsai]] soil. [[Bonsai]] enthusiasts use it as a soil additive, or pot a [[bonsai]] tree in 100% diatomaceous earth. Like [[perlite]], [[vermiculite]], and [[Hydroponics#Expanded clay|expanded clay]], it retains water and nutrients, while draining fast and freely, allowing high oxygen circulation within the growing medium.
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| ==== Marker in livestock nutrition experiments ====
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| Natural dried, not calcined 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:
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| :Where:
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| ::<math> \%N </math> is percent Nutrient Digestibility
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| ::<math> \%N_f </math> is the percent of nutrients in the feces
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| ::<math> \%N_F </math> is the percent of nutrients in the feed
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| ::<math> \%A_f </math> is the percent of AIA in the feces
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| ::<math> \%A_ F</math> is the percent of AIA in the feed
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| :And:
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| ::<math> \%N = \left ( 1 - \frac{\%N_f}{\%N_F} \right ) \times \left ( \frac{A_F}{A_f} \right ) \times 100 </math>
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| 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.
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| ==== Construction ====
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| Spent diatomaceous from the [[brewing]] process can be added to ceramic mass for the production of red bricks with higher open porosity.<ref>Ferraz et al., (2011), Manufacture of ceramic bricks using recycled brewing spent kieselguhr. Materials and Manufacturing Processes, 26 (10), 1319–1329. [http://dx.doi.org/10.1080/10426914.2011.551908 DOI: 10.1080/10426914.2011.551908]</ref>
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| == Specific varieties ==
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| *'''Tripolite''' is the variety found in [[Tripoli]], [[Libya]].
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| *'''Bann clay''' is the variety found in the [[River Bann|Lower Bann valley]] in [[Northern Ireland]].
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| *'''Moler''' ('''Mo-clay''') is the variety found in northwestern [[Denmark]], especially on the islands of [[Fur (island)|Fur]] and [[Mors (island)|Mors]].
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| *'''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 [[calcination|uncalcinated]], has a very fine particle size, and is very low in crystal silica (<2%).
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| *'''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 silica content (>60%).
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| == Microbial degradation ==
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| Certain species of bacteria in oceans and lakes can accelerate the rate of dissolution of silica in dead and living diatoms; by using [[hydrolytic]] enzymes to break down the organic algal material. <ref> {{citejournal|url=http://www.nature.com/nature/journal/v397/n6719/abs/397508a0.html|title=Accelerated dissolution of diatom silica by marine bacterial assemblages|author1=Kay D. Bidle|author2=Farooq Azam|journal=Nature|date=1999|volume=397|pages=508-512}}</ref> <ref> {{citeweb|url=http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0059977|title=The Structure of Microbial Community and Degradation of Diatoms in the Deep Near-Bottom Layer of Lake Baikal|date=2013}} </ref>
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| == Climatologic importance ==
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| The Earth's [[climate]] is affected by [[dust]] in the [[atmosphere]], so locating major sources of atmospheric dust is important for [[climatology]]. Recent research indicates that surface deposits of diatomaceous earth play an important role. For instance, the largest single atmospheric dust source is the [[Bodélé depression]] in [[Chad]], where storms push diatomite gravel over [[dune]]s, generating dust by [[abrasion (geology)|abrasion]].<ref name="WashingtonTodd2006">{{cite journal |last1=Washington |first1=R. |last2=Todd |first2=M. C. |last3=Lizcano |first3=G. |last4=Tegen |first4=I. |last5=Flamant |first5=C. |last6=Koren |first6=I. |last7=Ginoux |first7=P. |last8=Engelstaedter |first8=S. |last9=Bristow |first9=C. S. |last10=Zender |first10=C. S. |last11=Goudie |first11=A. S. |last12=Warren |first12=A. |last13=Prospero |first13=J. M. |title=Links between topography, wind, deflation, lakes and dust: The case of the Bodélé Depression, Chad |journal=Geophysical Research Letters |volume=33 |issue=9 |year=2006 |issn=0094-8276 |doi=10.1029/2006GL025827}}</ref>
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| == Safety considerations ==
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| Inhalation of ''crystalline'' silica is harmful to the lungs, causing [[silicosis]]. ''Amorphous'' silica is considered to be low toxicity, but prolonged inhalation cause changes to the lungs.<ref>http://www.cdc.gov/niosh/pel88/68855-54.html</ref> Diatomaceous earth is mostly amorphous silica, but contains some crystalline silica, especially in the saltwater forms.<ref>http://www.spca.bc.ca/assets/documents/welfare/professional-resources/farmer-resources/diatomaceous-earth-factsheet.pdf</ref> In a study of workers, those exposed to natural DE for over 5 years had no significant lung changes, while 40% of those exposed to the calcined form had developed [[pneumoconiosis]].<ref>http://www.cdc.gov/niosh/docs/81-123/pdfs/0552.pdf</ref> Today's common D.E. formulations are safer to use as they are predominantly made up of amorphous silica and contain little or no crystalline silica.<ref name="Inert Dusts"/>
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| The crystalline silica content of D.E. is regulated in the United States by the [[Occupational Safety and Health Administration]] (OSHA), and there are guidelines for the maximum amounts allowable in the product (1%) and in the air near the breathing zone of workers (6 mg/m3).<ref name="Inert Dusts">[http://www.oznet.ksu.edu/grsc_subi/Teaching/GRSC651/GRSC651_Courses_Material/lecture_slides/GRSC651_lect_20(1)_Inert_Dusts.pdf Inert Dusts] at [[Kansas State University]]</ref>
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| In the 1930s, long term occupational exposure among workers in the cristobalite D.E. industry who were exposed to high levels of airborne crystalline silica over decades were found to have an increased risk of [[silicosis]].<ref name="HughesWeill1998">{{cite journal |last1=Hughes |first1=Janet M. |last2=Weill |first2=Hans |last3=Checkoway |first3=Harvey |last4=Jones |first4=Robert N. |last5=Henry |first5=Melanie M. |last6=Heyer |first6=Nicholas J. |last7=Seixas |first7=Noah S. |last8=Demers |first8=Paul A. |title=Radiographic Evidence of Silicosis Risk in the Diatomaceous Earth Industry |journal=American Journal of Respiratory and Critical Care Medicine |volume=158 |issue=3 |year=1998 |pages=807–814 |issn=1073-449X |doi=10.1164/ajrccm.158.3.9709103}}</ref>
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| Today, workers are required to use respiratory-protection measures when concentrations of silica exceed allowable levels.
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| Diatomite produced for pool filters is treated with high heat ([[calcination]]) and a fluxing agent ([[soda ash]]), causing the formerly harmless amorphous silicon dioxide to assume its crystalline form.<ref name="Inert Dusts"/>
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| == The age and shape of diatoms ==
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| Each deposit of diatomaceous earth is different, with varying blends of pure diatomaceous earth combined with other natural clays and minerals.
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| The diatoms in each deposit contain different amounts of silica, depending on the age of the deposit. As well, the species of diatom may also differ among deposits.
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| The species of diatom is dependent upon the age and paleo-environment of the deposit. In turn, the shape of a diatom is determined by its species.
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| The shape of the diatoms contained in a deposit has not been proven to affect their functionality when it comes to the absorption of liquids, however certain applications, such as that for slugs and snails, do work best when a particular shaped diatom is used. 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]]s or [[nematodes]]. It may have some effect also on [[lophotrochozoan]]s, such as [[mollusk]]s or [[annelid]]s.
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| Many deposits throughout British Columbia, Canada, such as Red Lake Earth, are from the [[Miocene]] age and contain a species of diatom known as Melosira granulate. These diatoms are approximately 12 to 13 million years old and are a small globular shape.
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| A deposit containing diatoms from this age can provide many more benefits than that of an older deposit. For example, diatoms from the [[Eocene]] age (approximately 40 to 50 million years old) are not as effective in their ability to absorb fluids because older diatoms such as this recrystallize, their small pores becoming filled with silica.<ref>{{cite web |title=Diatoms |url=http://www.ucl.ac.uk/GeolSci/micropal/diatom.html |publisher=UCL London's Global University |accessdate=September 14, 2011}}</ref>
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| == See also ==
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| * [[Biomineralization]]
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| * [[Diatom]]
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| * [[Fuller's earth]]
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| * [[Perlite]]
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| * [[silica aerogel]]
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| * [[Zeolite]]
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| == References ==
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| {{Reflist|30em}}
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| == External links ==
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| *{{ICSC|0248|02}}
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| * [http://www.cdc.gov/niosh/npg/npgd0552.html CDC – NIOSH Pocket Guide to Chemical Hazards]
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| * [http://minerals.usgs.gov/minerals/pubs/commodity/diatomite/ Diatomite: Statistics and Information – USGS]
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| * [http://www.mindat.org/min-9855.html Tripolite: Tripolite mineral data] Citat: "...A diatomaceous earth consisting of opaline silica..."
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| * [http://www.eap.mcgill.ca/publications/eap4.htm DIATOMACEOUS EARTH: A Non Toxic Pesticide]
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| {{DEFAULTSORT:Diatomaceous Earth}}
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| [[Category:Sedimentary rocks]]
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| [[Category:Inorganic insecticides]]
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| [[Category:Soil improvers]]
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| [[Category:Fodder]]
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| [[Category:Fossils]]
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