Benstonite

{{Short description|Ba,Ca,Mg-mixed carbonate mineral}} {{Distinguish|Bentonite}} {{For|the rare chromium-rich ettringite, or Cr-AFt|Bentorite}} {{Infobox mineral | name = Benstonite | category = Carbonate minerals | image = Benstonite-Calcite-Fluorite-154901.jpg | imagesize = 260px | alt = | caption = Benstonite with calcite | formula = Ba6Ca6Mg(CO3)13<ref name=IMA2012>{{cite web|title=The New IMA List of Minerals – A Work in Progress – Update: November 2012|url=http://pubsites.uws.edu.au/ima-cnmnc/IMA_Master_List_(2012-11).pdf|work=Commission on New Minerals, Nomenclature and Classification|publisher=International Mineralogical Association|access-date=December 2, 2012|page=17|archive-url=https://web.archive.org/web/20130921060219/http://pubsites.uws.edu.au/ima-cnmnc/IMA_Master_List_(2012-11).pdf|archive-date=September 21, 2013|url-status=dead}}</ref> | IMAsymbol=Ben<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | molweight = | strunz = 5.AB.55 | dana = 14.2.3.1 | system = Trigonal | class = Rhombohedral ({{overbar|3}}) H-M group: ({{overbar|3}}) | symmetry = ''R''{{overbar|3}} | unit cell = a = 18.280 Å, c = 8.652 Å; Z = 3 | color = Snow-white, ivory, very pale yellow, pale yellowish brown<ref name=handbook/> | habit = | twinning = | cleavage = Good on {31{{overbar|4}}2}<ref name=handbook/> | fracture = | tenacity = | mohs = 3–4 | luster = Vitreous | polish = | refractive = nω = 1.690 nε = 1.527 | opticalprop = Uniaxial (−) | birefringence = δ = 0.163 | 2V = | dispersion = | pleochroism = | fluorescence= Red or yellow under UV and X-rays<ref name=handbook>{{cite encyclopedia|url=http://www.handbookofmineralogy.org/pdfs/benstonite.pdf |title=Benstonite |encyclopedia=Handbook of Mineralogy |editor1-first=John W. |editor1-last=Anthony|editor2-first=Richard A. |editor2-last=Bideaux|editor3-first=Kenneth W. |editor3-last=Bladh|editor4-first= Monte C. |editor4-last=Nichols |publisher=Mineralogical Society of America|location=Chantilly, VA}}</ref> | absorption = | streak = White | gravity = | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Translucent | other = | references =<ref name=mindat>{{cite web|title=Benstonite|url=http://www.mindat.org/min-626.html|publisher=Mindat|access-date=December 2, 2012}}</ref> }} '''Benstonite''' is a mineral with formula Ba6Ca6Mg(CO3)13.<ref name=IMA2012/> Discovered in 1954, the mineral was described in 1961 and named after Orlando J. Benston (1901–1966).

==Description and occurrence== Benstonite is translucent and white, pale yellow, or pale yellow-brown in color.<ref name=handbook/> The mineral occurs as cleavable masses; cleavage fragments are nearly perfectly rhombohedral in shape. Cleavage faces are up to {{convert|1|cm|in|abbr=on}} across and slightly curved. On large specimens, the faces exhibit a mosaic structure similar to that in some specimens of dolomite and siderite.{{sfn|Lippmann|1962|p=586}} Benstonite fluoresces red or yellow under x-rays and longwave and shortwave ultraviolet. The mineral also exhibits strong red phosphorescence.<ref name=handbook/>

Benstonite is known to occur in Canada, China, India, Italy, Namibia, Russia, Sweden, and the United States.<ref name=mindat/> It occurs in association with alstonite, barite, barytocalcite, calcite, daqingshanite, fluorite, huntite, monazite, phlogopite, pyrite, sphalerite, strontianite, and quartz.<ref name=handbook/>

==Synthesis== The mineral was first synthesized in 1973 during a study of the Ba-Mg-Ca-CO3 system in aqueous solution. At room temperature, a solution containing proportional quantities of magnesium chloride, barium chloride, and calcium chloride was prepared, to which sodium carbonate was added. The solution immediately precipitated, and after sitting for two weeks, the precipitate was identified as nearly pure benstonite.{{sfn|Hood|Steidl|1973|p=341}}

==History== Orlando J. Benston<ref name=mindat/> of Malvern, Arkansas, visited a barite mine near the Magnet Cove igneous complex on New Year's Eve, 1954. He collected samples of a mineral that he guessed might be alstonite or barytocalcite on the basis of qualitative tests.{{sfn|Lippmann|1962|pp=585–586}} Friedrich Lippmann identified it as a new mineral and described it in the journal ''Naturwissenschaften'' in 1961.<ref>{{cite journal|last=Fleischer|first=Michael|title=New mineral names|journal=The American Mineralogist|date=November–December 1961|volume=46|issue=11–12|url=http://www.minsocam.org/ammin/AM46/AM46_1513.pdf|page=1517}}</ref> He named it Benstonite in honor of Benston.{{sfn|Lippmann|1962|p=586}}

Type specimens are held at Victor Goldschmidt University in Germany and the National Museum of Natural History in the United States.<ref name=handbook/>

==References== {{Reflist|30em}}

;Bibliography *{{cite journal|last1=Hood|first1=William C.|last2=Steidl|first2=Peter F.|title=Synthesis of Benstonite at Room Temperature|journal=American Mineralogist|date=March–April 1973|volume=58|issue=3–4|pages=341–342|url=http://www.minsocam.org/ammin/AM58/AM58_341.pdf}} *{{cite journal|last=Lippmann|first=Friedrich|title=Benstonite, Ca7Ba6(CO3)13, a new Mineral from the Barite Deposit in Hot Spring County, Arkansas|journal=The American Mineralogist|date=May–June 1962|volume=47|issue=5–6|pages=585–598|url=http://www.minsocam.org/ammin/AM47/AM47_585.pdf}}

==Further reading== *{{cite journal|last1=Konev|first1=A. A.|title=Mg-deficient strontium benstonite from the ore occurrence biraya (Siberia)|journal=Zapiski Vserossijskogo mineralogičeskogo obŝestva|year=2004|volume=133|issue=6|pages=65–73|url=http://rruff.info/uploads/ZVMO133N6_65.pdf|language=Russian}}

==External links== {{commonscat-inline|Benstonite}}

Category:Trigonal minerals Category:Minerals in space group 148 Category:Carbonate minerals Category:Magnesium minerals Category:Calcium minerals Category:Barium minerals