Editing Phosphorite

{{Short description|Sedimentary rock containing large amounts of phosphate minerals}}
[[File:Peloidal phosphorite Phosphoria Formation Simplot Mine Idaho.jpg|thumb|Peloidal phosphorite, [[Phosphoria Formation]], Simplot Mine, Idaho. 4.6 cm wide.]]
[[File:Fossiliferous peloidal phosphorite, Yunnan Province China.jpg|thumb|Fossiliferous peloidal phosphorite, (4.7 cm across), [[Yunnan]], [[China]]. ]]
'''Phosphorite''', '''phosphate rock''' or '''rock phosphate''' is a non-[[detrital]] [[sedimentary rock]] that contains high amounts of [[phosphate minerals]]. The phosphate content of phosphorite (or grade of phosphate rock) varies greatly, from 4%<ref name="fao">{{cite book |last1=Zapata |first1=F. |last2=Roy |first2=R.N. |date=2004 |title=Use of Phosphate Rocks for Sustainable Agriculture |url=http://www.fao.org/3/y5053e/y5053e00.htm#Contents |chapter=Chapter 1 - Introduction: Phosphorus in the soil-plant system |chapter-url=http://www.fao.org/3/y5053e/y5053e06.htm |location=Rome |publisher=[[Food and Agriculture Organization]] |isbn=92-5-105030-9}}</ref> to 20% [[phosphorus pentoxide]] (P<sub>2</sub>O<sub>5</sub>). Marketed phosphate rock is enriched ("beneficiated") to at least 28%, often more than 30% P<sub>2</sub>O<sub>5</sub>. This occurs through washing, screening, de-liming, magnetic separation or flotation.<ref name="fao" /> By comparison, the average phosphorus content of sedimentary rocks is less than 0.2%.<ref name=Blatt>Blatt, Harvey and Robert J. Tracy, ''Petrology'', Freeman, 1996, 2nd ed. pp. 345–349 {{ISBN|0-7167-2438-3}}</ref>  

The phosphate is present as [[fluorapatite]] Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>F typically in [[cryptocrystalline]] masses (grain sizes < 1 μm) referred to as [[collophane]]-sedimentary apatite deposits of uncertain origin.<ref name=Blatt/> It is also present as [[hydroxyapatite]] Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>OH or Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>(OH)<sub>2</sub>, which is often dissolved from vertebrate bones and teeth, whereas fluorapatite can originate from [[hydrothermal vein]]s. Other sources also include chemically dissolved phosphate minerals from [[igneous]] and [[metamorphic rock]]s. Phosphorite deposits often occur in extensive layers, which cumulatively cover tens of thousands of square kilometres of the [[Crust (geology)|Earth's crust]].<ref>C.Michael Hogan. 2011. [http://www.eoearth.org/article/Phosphate?topic=49557 ''Phosphate''. Encyclopedia of Earth. Topic ed. Andy Jorgensen. Ed.-in-Chief C.J.Cleveland. National Council for Science and the Environment. Washington DC]</ref>

[[Limestone]]s and [[mudstone]]s are common phosphate-bearing rocks.<ref name="Prothero">{{cite book|author1=Prothero, Donald R.  |author2=Schwab, Fred |title=Sedimentary Geology|url=https://books.google.com/books?id=vlG-BGZhZrAC|access-date=15 December 2012|date=22 August 2003|publisher=Macmillan|isbn=978-0-7167-3905-0|pages=265–269}}</ref> Phosphate-rich sedimentary rocks can occur in dark brown to black beds, ranging from centimeter-sized laminae to beds that are several meters thick. Although these thick beds can exist, they are rarely only composed of phosphatic sedimentary rocks. Phosphatic sedimentary rocks are commonly accompanied by or interbedded with [[shale]]s, [[chert]]s, limestone, [[Dolomite (rock)|dolomite]]s and sometimes [[sandstone]].<ref name="Prothero"/> These layers contain the same textures and structures as fine-grained limestones and may represent [[diagenesis|diagenetic]] replacements of [[carbonate minerals]] by phosphates.<ref name=Blatt/> They also can be composed of peloids, ooids, fossils, and clasts that are made up of apatite. There are some phosphorites that are very small and have no distinctive granular textures. This means that their textures are similar to that of collophane, or fine [[micrite]]-like texture. Phosphatic grains may be accompanied by [[organic matter]], [[clay mineral]]s, [[silt]]-sized detrital grains, and [[pyrite]]. Peloidal or pelletal phosphorites occur normally; whereas [[Oolite|oolitic]] phosphorites are not common.<ref name="Prothero"/>

Phosphorites are known from [[Proterozoic]] [[banded iron formation]]s in [[Australia]], but are more common from [[Paleozoic]] and [[Cenozoic]] sediments. The [[Permian]] [[Phosphoria Formation]] of the western [[United States]] represents some 15 million years of sedimentation. It reaches a thickness of 420 metres and covers an area of 350,000&nbsp;km<sup>2</sup>.<ref name=Blatt/> Commercially mined phosphorites occur in [[France]], [[Belgium]], [[Spain]], [[Morocco]], [[Tunisia]], [[Saudi Arabia]]<ref name="Galmed_et_al_2020">{{cite journal | title=Petrology of Early Paleogene phosphorite deposits in Hazm Al-Jalamid, Northwest Saudi Arabia | last1=Galmed | first1=M.A. | last2=Nasr | first2=M.M. | last3=Khater | first3=A.E-S.M. | journal=Arabian Journal of Geosciences | date=2020 | volume=13 | issue=17 | at=829 | doi=10.1007/s12517-020-05852-3| s2cid=221200370 }}</ref> and [[Algeria]]. In the United States phosphorites have been mined in [[Florida]], [[Tennessee]], [[Wyoming]], [[Utah]], [[Idaho]] and [[Kansas]].<ref>Klein, Cornelis and Cornelius S. Hurlbut, Jr., ''Manual of Mineralogy'', Wiley, 1985, 20th ed., p. 360, {{ISBN|0-471-80580-7}}</ref>

==Classification of phosphatic sedimentary rocks==

(1) ''Pristine:'' Phosphates that are in pristine conditions have not undergone [[bioturbation]]. In other words, the word pristine is used when phosphatic sediment, phosphatized [[stromatolite]]s and phosphate [[hardground]]s have not been disturbed.<ref name="Middleton"/>

(2) ''Condensed:'' Phosphatic particles, laminae and beds are considered condensed when they have been concentrated. This is helped by the extracting and reworking processes of phosphatic particles or bioturbation.<ref name="Middleton"/>

(3) ''Allochthonous:'' Phosphatic particles that were moved by turbulent or gravity-driven flows and deposited by these flows.<ref name="Middleton"/>

==Phosphorus cycle, formation and accumulation==
{{Main|Phosphorus cycle}}
The heaviest accumulation of phosphorus is mainly on the [[Seabed|ocean floor]]. Phosphorus accumulation occurs from atmospheric [[precipitation]], dust, glacial runoff, cosmic activity, underground hydrothermal volcanic activity, and deposition of organic material. The primary inflow of dissolved phosphorus is from continental weathering, brought out by rivers to the ocean.<ref name="Delaney">{{cite journal|doi=10.1029/98GB02263 |author=Delaney, M.L.|author-link=Margaret Delaney|year=1998|title= Phosphorus Accumulation in Marine Sediments and Oceanic Phosphorus Cycle|journal= Global Biogeochemical Cycles|volume= 12|pages= 563–572|issue=4|bibcode=1998GBioC..12..563D|doi-access=free}}</ref> It is then processed by both micro- and macro-organisms. Diatomaceous plankton, phytoplankton, and zooplankton process and dissolve phosphorus in the water. The bones and teeth of certain fish (e.g. anchovies) absorb phosphorus and are later deposited and buried in the [[marine sediment]].<ref name="Baturin">Baturin, G.N, Phosphorites on the Sea Floor: Origin, Composition and Distribution. Elsevier. 1981, New York, pp. 24–50 {{ISBN|044441990X}}.</ref>

Depending on the pH and salinity levels of the ocean water, organic matter will decay, releasing phosphorus from sediment in shallow basins. Bacteria and enzymes dissolve organic matter on the water–bottom interface, thus returning phosphorus to the beginning of its biogenic cycle. Mineralization of organic matter can also cause the release of phosphorus back into the ocean water.<ref name="Baturin"/>

==Depositional environments==

Phosphates are known to be deposited in a wide range of [[depositional environment]]s. Normally phosphates are deposited in very shallow, near-shore marine or low energy environments. This includes environments such as supratidal zones, littoral or intertidal zones, and most importantly estuarine.<ref name="Baturin"/> Currently, areas of oceanic upwelling cause the formation of phosphates. This is because of the constant stream of phosphate brought from the large, deep ocean reservoir (see below). This cycle allows continuous growth of organisms.<ref name="Middleton"/>

''Supratidal zones:'' Supratidal environments are part of the tidal flat system where the presence of strong wave activity is non-existent. Tidal flat systems are created along open coasts and relatively low wave energy environments. They can also develop on high energy coasts behind barrier islands where they are sheltered from the high energy wave action. Within the tidal flat system, the supratidal zone lies in a very high tide level. However, it can be flooded by extreme tides and cut across by tidal channels. This is also subaerially exposed, but is flooded twice a month by spring tides.<ref name="Boggs">Boggs, Sam, Jr. (2006). ''Principles of Sedimentology and Stratigraphy'' (4th ed.), Pearson Education Inc., Upper Saddle River, NJ, pp. 217–223 {{ISBN|0321643186}}</ref>

''Littoral environments/intertidal zones:'' Intertidal zones are also part of the tidal flat system. The intertidal zone is located within the mean high and low tide levels. It is subject to tidal shifts, which means that it is subaerially exposed once or twice a day. It is not exposed long enough to support the growth of most vegetation. The zone contains both suspension sedimentation and bed load.<ref name="Boggs"/>

''Estuarine environments'': Estuarine environments, or estuaries, are located at the lower parts of rivers that flow into the open sea. Since they are in the seaward section of the drowned valley system they receive sediment from both marine and fluvial sources. These contain facies that are affected by tide and wave fluvial processes. An estuary is considered to stretch from the landward limit of tidal facies to the seaward limit of coastal facies. Phosphorites are often deposited in fjords within estuarine environments. These are estuaries with shallow sill constrictions. During Holocene sea-level rise, fjord estuaries formed by drowning of glacially-eroded U-shaped valleys.<ref name="Boggs"/>

The most common occurrence of phosphorites is related to strong marine upwelling of sediments. Upwelling is caused by deep water currents that are brought up to coastal surfaces where a large deposition of phosphorites may occur. This type of environment is the main reason why phosphorites are commonly associated with silica and chert. Estuaries are also known as a phosphorus “trap”. This is because coastal estuaries contain a high productivity of phosphorus from marsh grass and benthic algae which allow an equilibrium exchange between living and dead organisms.<ref name="D.R Pevear">{{cite journal|title=The estuarine formation of United States Atlantic Coastal Plain phosphorite |url=http://econgeol.geoscienceworld.org/content/61/2/251.abstract<!--broken doi-->|author=Pevear, D. R.|journal=Economic Geology|year= 1966|volume= 61|issue=2|pages=251–256|doi=10.2113/gsecongeo.61.2.251|bibcode=1966EcGeo..61..251P |url-access=subscription}}</ref>

===Types of phosphorite deposition===

*Phosphate nodules: These are spherical concentrations that are randomly distributed along the floor of continental shelves. Most phosphorite grains are sand size although particles greater than 2&nbsp;mm may be present. These larger grains, referred to as [[Nodule (geology)|nodules]], can range up to several tens of centimeters in size. Phosphate nodules are known to occur in significant quantities offshore northern [[Chile]].<ref>{{Cite journal|title=Potential mineral resources of the Chilean offshore: an overview|journal=[[Andean Geology]]|url=http://www.andeangeology.cl/index.php/revista1/article/view/V47n1-3260/html|last1=García|first1=Marcelo|volume=47|pages=1–13|last2=Correa|first2=Jorge|issue=1|year=2020|last3=Maksaev|first3=Víctor|last4=Townley|first4=Brian|doi=10.5027/andgeoV47n1-3260|doi-access=free}}</ref> 
[[File:Estonian shelly phosphorites.jpg|thumb|right|Shelly phosphorite from Estonia]]
*Bioclastic phosphates or bone beds: Bone beds are bedded phosphate deposits that contain concentrations of small skeletal particles and coprolites.<ref name="Prothero"/> Some also contain invertebrate fossils like brachiopods and become more enriched in P<sub>2</sub>O<sub>5</sub> after diagenetic processes have occurred. Bioclastic phosphates can also be cemented by phosphate minerals.<ref name="Baturin"/> 
*Phosphatization: Phosphatization is a type of rare diagenetic processes. It occurs when fluids that are rich in phosphate are leached from guano.<ref name="Prothero"/> These are then concentrated and reprecipitated in limestone. Phosphatized fossils or fragments of original phosphatic shells are important components within some these deposits.

====Tectonic and oceanographic settings of marine phosphorites====

*Epeiric sea phosphorites: [[Epeiric sea]] phosphorites are within marine shelf environments. These are in a broad and shallow cratonic setting. This is where granular phosphorites, phosphorite hardgrounds, and nodules occur.<ref name="Middleton">Middleton V. Gerald, 2003 Encyclopedia of Earth Sciences series. Encyclopedia of Sediment and Sedimentary Rocks. Kluwer Academic Publishers. Dordrect, Boston, London. pp 131, 727, 519–524.</ref>
*Continental margin phosphorites: Convergent, passive, upwelling, non-upwelling. This environment accumulates phosphorites in the form of hardgrounds, nodules and granular beds.<ref name="D.R Pevear"/> These accumulate by carbonate fluorapatite precipitation during early diagenesis in the upper few tens of centimeters of sediment. There are two different environmental conditions in which phosphorites are produced within continental margins. Continental margins can consist of organic rich sedimentation, strong coastal upwelling, and pronounced low oxygen zones. They can also form in conditions such as oxygen rich bottom waters and organic poor sediments.<ref name="Middleton"/>
*Seamount phosphorites: These are phosphorites that occur in seamounts, guyots, or flat topped seamounts, seamount ridges. These phosphorites are produced in association with iron and magnesium bearing crusts. In this setting the productivity of phosphorus is recycled within an iron oxidation reduction phosphorus cycle. This cycle can also form glauconite which is normally associated with modern and ancient phosphorites.<ref name="Middleton"/>
*Insular phosphorites: Insular phosphorites are located in carbonate islands, plateaus, coral island consisting of a reef surrounding a lagoon or, atoll lagoon, marine lakes. The phosphorite here originates from guano. Replacement of deep sea sediments precipitates, that has been formed in place on the ocean floor.<ref name="Middleton"/>

==Production and use==
[[File:DSCN5766-guano-glantz crop b.jpg|thumb|upright|Guano phosphorite mining in the [[Chincha Islands]] of Peru, c. 1860]]
[[File:Phosphorite Mine Oron Israel 070313.jpg|thumb|Phosphorite mine near Oron, Negev, Israel.]]

{{Further|Peak phosphorus}}

===Production===
Deposits which contain phosphate in quantity and concentration which are economic to [[Mining|mine]] as [[ore]] for their phosphate content are not particularly common. The two main sources for phosphate are [[guano]], formed from [[bird]] or [[bat]] droppings, and rocks containing concentrations of the calcium phosphate mineral, [[apatite]].

{{As of|2006}}, the US is the world's leading producer and exporter of phosphate fertilizers, accounting for about 37% of world P<sub>2</sub>O<sub>5</sub> exports.<ref>[http://minerals.usgs.gov/minerals/pubs/commodity/phosphate_rock/myb1-2006-phosp.pdf US Geological Survey Minerals Yearbook 2006 Rock Phosphate]</ref> {{As of|2018|December}}, the world's total economic demonstrated resource of rock phosphate is 70 [[Tonne|gigatonne]]s,<ref>{{cite report |url= https://d28rz98at9flks.cloudfront.net/132457/132457_00_0.pdf |title= AIMR Report 2019 |page= 10}}</ref> which occurs principally as [[sedimentary]] marine phosphorites.<ref name="AIMR Report 2013"/>

{{As of|2012}}, [[China]], the [[United States]] and [[Morocco]] are the world's largest miners of phosphate rock, with a production of 77 [[Tonne|megatonne]]s, 29.4 Mt and 26.8 Mt (including 2.5 Mt in the [[Sahara]] of Morocco) respectively in 2012 while global production reached 195 Mt.<ref>[http://www.fertilizer.org IFA 2012 statistics]</ref> It is thought that in India there are almost 260 million tons of rock phosphate.<ref name=":4">{{Cite journal |last1=Cordell |first1=Dana |author-link=Dana Cordell |last2=White |first2=Stuart |date=2013-01-31 |title=Sustainable Phosphorus Measures: Strategies and Technologies for Achieving Phosphorus Security |journal=Agronomy |volume=3 |issue=1 |pages=86–116 |doi=10.3390/agronomy3010086 |doi-access=free|hdl=10453/24038 |hdl-access=free }}</ref> Other countries with significant production include [[Brazil]], [[Russia]], [[Jordan]] and [[Tunisia]]. Historically, large amounts of phosphates were obtained from deposits on small islands such as [[Christmas Island]] and [[Nauru]], but these sources are now largely depleted.

Phosphate ore is mined and beneficiated into rock phosphate. [[Beneficiation]] of phosphate ore is a process which includes washing, flotation and calcining.<ref name="fao"/> [[Froth flotation]] is used to concentrate the mined ore to rock phosphate. The mined ore is crushed and washed, creating a slurry, this ore slurry is then treated with [[fatty acids]] to cause calcium phosphate to become [[hydrophobic]].

This rock phosphate is then either solubilized to produce wet-process [[phosphoric acid]], or smelted to produce elemental [[phosphorus]]. Phosphoric acid is reacted with phosphate rock to produce the fertilizer triple [[superphosphate]] or with [[anhydrous ammonia]] to produce the [[ammonium phosphate]] fertilizers.  Elemental phosphorus is the base for furnace-grade phosphoric acid, phosphorus pentasulfide, [[phosphorus pentoxide]], and [[phosphorus trichloride]].{{Citation needed|date=October 2019}}

===Uses===
Approximately 90% of rock phosphate production is used for [[fertilizer]] and animal feed supplements and the balance for industrial chemicals.<ref name="fao"/> In addition, phosphorus from rock phosphate is also used in food preservatives, baking flour, pharmaceuticals, anticorrosion agents, cosmetics, fungicides, insecticides, detergents, ceramics, water treatment and metallurgy.<ref name="AIMR Report 2013">{{cite report |last= Britt |first= Allison |chapter-url= https://d28rz98at9flks.cloudfront.net/78988/78988_AIMR_2013.pdf |chapter=Phosphate |title= AIMR Report 2013 |page= 90}}</ref>

For use in the [[chemical fertilizer]] industry, beneficiated rock phosphate must be concentrated to levels of at least 28% phosphorus pentoxide (P<sub>2</sub>O<sub>5</sub>), although most marketed grades of phosphate rock are 30% or more.<ref name="fao"/>

It must also have reasonable amounts of calcium carbonate (5%), and <4% combined [[iron]] and [[aluminium]] oxides.{{Citation needed|date=October 2019}} Worldwide, the resources of high-grade ore are declining, and use of lower grade ore may become more attractive.<ref name="fao"/>

Beneficiated rock phosphate is also marketed and accepted as an [[Organic agriculture|"organic"]] alternative to "chemical" phosphate fertilizer which has been further concentrated from it, because it is perceived as being more "natural". According to a report for the FAO, it can be more [[Sustainable agriculture|sustainable]] to apply rock phosphate as a fertilizer in certain soil types and countries, although it has many drawbacks. According to the report it may have higher sustainability compared to more concentrated fertilizers because of reduced manufacturing costs and the possibility of local procurement of the refined ore.<ref name="fao"/>

Rare earth elements are being found within phosphorites. With increasing demand from modern technology a different method of finding rare earth elements, independent of China, is becoming increasingly important. With yields greater than those from deposits in China, phosphorites offer a new resource located within the U.S. that would likely lead to independence from influence of countries outside of the U.S.<ref>{{cite journal | doi=10.1016/j.gr.2014.10.008 | title=Rare earth elements in sedimentary phosphate deposits: Solution to the global REE crisis? | year=2015 | last1=Emsbo | first1=Poul | last2=McLaughlin | first2=Patrick I. | last3=Breit | first3=George N. | last4=Du Bray | first4=Edward A. | last5=Koenig | first5=Alan E. | journal=Gondwana Research | volume=27 | issue=2 | pages=776–785 | bibcode=2015GondR..27..776E | doi-access=free }}</ref>

==See also==
* [[Phosphate mining in the United States]]

==References==
{{reflist|35em}}

==External links==
{{Commons category multi | Phosphate mines | Phosphate minerals}}
* [http://minerals.usgs.gov/minerals/pubs/commodity/phosphate_rock  US Geological Survey]
* [http://minerals.usgs.gov/minerals/pubs/commodity/phosphate_rock/stat  USGS Statistics]
* [http://www.pir.sa.gov.au/minerals/geology/commodities/phosphate   PIRSA website]
* [http://www.fertilizer.org   International Fertilizer Industry Association]
* [https://www.sciencedirect.com/science/article/pii/S1342937X14003128?via%3Dihub Science Direct]
{{Rock type}}
[[Category:Economic geology]]
[[Category:Sedimentary rocks]]
[[Category:Phosphorus]]
[[Category:Phosphate minerals]]
[[Category:Industrial minerals]]