Editing Strontium (section)

==Occurrence==
{{Category see also|Strontium minerals}}
[[Image:Celestine Poland.jpg|thumb|left|The mineral celestine (SrSO<sub>4</sub>)]]

Strontium commonly occurs in nature, being the 15th most [[Abundance of the chemical elements|abundant element]] on Earth (its heavier congener barium being the 14th), estimated to average approximately 360&nbsp;[[parts per million]] in the [[Abundance of elements in Earth's crust|Earth's crust]]<ref>{{cite journal|last1=Turekian|first1=K. K.|last2=Wedepohl|first2=K. H.|title=Distribution of the elements in some major units of the Earth's crust|journal=Geological Society of America Bulletin|volume=72|issue=2|pages=175–92|doi=10.1130/0016-7606(1961)72[175:DOTEIS]2.0.CO;2|bibcode = 1961GSAB...72..175T |year=1961|doi-access=free}}</ref> and is found chiefly as the [[sulfate]] [[mineral]] [[Celestine (mineral)|celestine]] (SrSO<sub>4</sub>) and the [[carbonate]] [[strontianite]] (SrCO<sub>3</sub>). Of the two, celestine occurs much more frequently in deposits of sufficient size for mining. Because strontium is used most often in the carbonate form, strontianite would be the more useful of the two common minerals, but few deposits have been discovered that are suitable for development.<ref name="usgs10">{{cite web |publisher = United States Geological Survey |access-date = 14 May 2010 |title = Mineral Commodity Summaries 2010: Strontium |first = Joyce A. |last = Ober |url = http://minerals.usgs.gov/minerals/pubs/commodity/strontium/mcs-2010-stron.pdf }}</ref> Because of the way it reacts with air and water, strontium only exists in nature when combined to form minerals. Naturally occurring strontium is stable, but its synthetic isotope Sr-90 is only produced by nuclear fallout.

In groundwater strontium behaves chemically much like calcium. At intermediate to acidic [[pH]] Sr<sup>2+</sup> is the dominant strontium species. In the presence of calcium ions, strontium commonly forms [[Coprecipitation|coprecipitates]] with calcium minerals such as [[calcite]] and anhydrite at an increased pH. At intermediate to acidic pH, dissolved strontium is bound to soil particles by [[Cation-exchange capacity|cation exchange]].<ref name="Heuel-Fabianek">{{cite journal |journal=Berichte des Forschungszentrums Jülich |volume=4375 |date=2014 |author=Heuel-Fabianek, B. |title= Partition Coefficients (Kd) for the Modelling of Transport Processes of Radionuclides in Groundwater | url = http://juser.fz-juelich.de/record/154001/files/FZJ-2014-03430.pdf | issn=0944-2952 }}</ref>

The mean strontium content of ocean water is 8&nbsp;mg/L.<ref>{{cite book|chapter=Strontium|title=Artesian water in Tertiary limestone in the southeastern States |chapter-url = https://books.google.com/books?id=8eQqAQAAIAAJ&pg=PA138| pages =138–39 |series = Geological Survey Professional Paper|publisher=United States Government Printing Office|author=Stringfield, V. T. |date = 1966}}</ref><ref>{{cite journal | doi = 10.1016/0009-2541(66)90013-1 | title = Observed variations in the strontium concentration of sea water | date = 1966 | last1 = Angino | first1 = Ernest E. | last2 = Billings | first2 = Gale K. | last3 = Andersen | first3 = Neil | journal = Chemical Geology | volume = 1 | page = 145| bibcode = 1966ChGeo...1..145A }}</ref> At a concentration between 82 and 90 μmol/L of strontium, the concentration is considerably lower than the calcium concentration, which is normally between 9.6 and 11.6&nbsp;mmol/L.<ref>{{cite journal | doi = 10.1007/s00338-004-0467-x | title = Influence of seawater Sr content on coral Sr/Ca and Sr thermometry | date = 2005 | last1 = Sun | first1 = Y. | last2 = Sun | first2 = M. | last3 = Lee | first3 = T. | last4 = Nie | first4 = B. | journal = Coral Reefs | volume = 24 | page = 23| s2cid = 31543482 }}</ref><ref>{{cite book |url = https://books.google.com/books?id=zNicdkuulE4C&pg=PA928 |title = Industrial Minerals & Rocks: Commodities, Markets, and Uses |isbn = 978-0-87335-233-8 |last1 = Kogel |first1 = Jessica Elzea |last2 = Trivedi |first2 = Nikhil C. |last3 = Barker |first3 = James M. |date = 5 March 2006}}</ref> It is nevertheless much higher than that of barium, 13&nbsp;μg/L.<ref name="CRC" />