{{Short description|Nesosilicate mineral}} {{infobox mineral | name = Bultfonteinite | category = Nesosilicates | image = Bultfonteinite - Linxi, Chifeng City, Inner Mongolia, China.jpg | imagesize = 260px | caption = Bultfonteinite from Shijiangshan mine, China | formula = Ca<sub>2</sub>SiO<sub>2</sub>(OH,F)<sub>4</sub> | IMAsymbol=Bul<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 = 9.AG.80<ref name=mindat/> | dana = 52.4.7.2<ref name=mindat/> | system = Triclinic | class = Pinacoidal ({{overbar|1}})<br/><small>(same H-M symbol)</small> | symmetry = ''P''{{overbar|1}} | unit cell = a = 10.99&nbsp;Å, b = 8.18&nbsp;Å<br/>c = 5.67&nbsp;Å, α = 93.95°<br/>β = 91.32°, γ = 89.85°;<ref name=mindat/> Z&nbsp;=&nbsp;4 | color = Colorless, pink, light brown | habit = | twinning = Interpenetrating on {100} and {010}; polysynthetic | cleavage = Good on {100} and {010} | fracture = Conchoidal | tenacity = | mohs = 4.5 | luster = Vitreous | polish = | refractive = n<sub>α</sub> = 1.587<br>n<sub>β</sub> = 1.590<br>n<sub>γ</sub> = 1.597<ref name=mindat/> | opticalprop = Biaxial (+) | birefringence = δ = 0.010<ref name=mindat/> | 2V = 70° (measured) | dispersion = r > v; barely perceptible | pleochroism = | fluorescence= | absorption = | streak = White<ref name=mindat>{{cite web |title=Bultfonteinite |url=http://www.mindat.org/min-800.html |publisher=Mindat |access-date=July 19, 2012 |archive-date=November 14, 2009 |archive-url=https://web.archive.org/web/20091114021049/http://www.mindat.org/min-800.html |url-status=live }}</ref> | gravity = | density = | melt = | fusibility = | diagnostic = | solubility = Soluble in hydrochloric acid<ref name=newNames>{{cite journal |last=Foshag |first=W. F. |title=New Mineral Names: Bulfonteinite |journal=American Mineralogist |date=January 1933 |volume=18 |issue=1 |url=http://www.minsocam.org/ammin/AM18/AM18_31.pdf |page=32 |publisher=Mineralogical Society of America |access-date=2012-07-19 |archive-date=2012-07-23 |archive-url=https://web.archive.org/web/20120723012852/http://www.minsocam.org/ammin/AM18/AM18_31.pdf |url-status=live }}</ref> | diaphaneity = Transparent | references =<ref name=handbook>{{cite web |title=Bultfonteinite |url=http://www.handbookofmineralogy.org/pdfs/bultfonteinite.pdf |work=Handbook of Mineralogy |publisher=Mineral Data Publishing |access-date=July 19, 2012 |archive-date=August 1, 2012 |archive-url=https://web.archive.org/web/20120801114800/http://www.handbookofmineralogy.org/pdfs/bultfonteinite.pdf |url-status=live }}</ref> }}

'''Bultfonteinite''', originally '''dutoitspanite''', is a pink, light-brown or colorless mineral with chemical formula Ca<sub>2</sub>SiO<sub>2</sub>(OH,F)<sub>4</sub>. It was discovered in 1903 or 1904 in the Bultfontein mine in South Africa, for which the mineral is named, and described in 1932.

==Description== thumb|left|Acicular crystals from the Wessels Mine in South Africa

Bultfonteinite is transparent and ranges from pale pink or light brown to colorless.<ref>{{cite book |url=https://books.google.com/books?id=Xp9nEAAAQBAJ&pg=PA175 |page=175 |title=Minerals & Gemstones of Southern Africa |first=Bruce |last=Cairncross |publisher=Penguin Random House South Africa |year=2022 |isbn=978-1-77584-754-0 }}</ref> The mineral occurs as radiating prismatic acicular crystals and radial spherules up to {{cvt|2|cm|in|1}}.<ref name=handbook/>

==Structure== The crystal structure of bultfonteinite consists of strips of [Ca<sub>4</sub>Si<sub>2</sub>O<sub>4</sub>]<sup>8+</sup>, that run along the 5.67 Å ''c''-axis, held together by Ca–O–Ca, Ca–F–Ca, Ca–H<sub>2</sub>O–Ca, and Ca–O–Si bonds. Silicon atoms occur in isolated tetrahedra and the calcium atoms have seven-fold coordination, derived from a triangular prism with a seventh atom present on one of the square faces.{{sfn|McIver|1963|p=551}}

==History== In either 1903 or 1904, a miner discovered the first specimen of bultfonteinite on the 480-foot level of the Bultfontein mine in Kimberley, South Africa. The mineral occurred in a several-hundred-foot-tall horse of kimberlite-enclosed dolerite and shale fragments. The specimen, mistakenly thought to be natrolite, was given to Alpheus F. Williams. Several years later, additional samples were found by C. E. Adams in the nearby Dutoitspan mine and given to the MacGregor Museum in Kimberley.{{sfn|Parry|Williams|Wright|1932|p=145}} Shortly before 1932, the mineral was found about {{convert|100|mi|km}} to the southeast of Kimberley at the Jagersfontein Mine in Orange River Colony.{{sfn|Parry|Williams|Wright|1932|p=145}}{{sfn|Murdoch|1955|p=900}}

After John Parry and F. E. Wright described the mineral afwillite in 1925, Williams recognized that his samples of bultfonteinite were not natrolite, but were likely a new mineral species. Chemical analysis by John Parry and crystallographic and optical determination by Wright proved it to be a new mineral.{{sfn|Parry|Williams|Wright|1932|p=146}} The mineral was described by Parry, Williams, and Wright in 1932 and named ''bultfonteinite''.{{sfn|Parry|Williams|Wright|1932|p=145}} Their original description does not explicitly state the origin of the name, but it is presumably named after the mine in which it was discovered.<ref name=newNames/> Earlier that year in his book ''The Genesis of the Diamond'', Williams had called the mineral dutoitspanite, a name which was "apparently discarded".{{sfn|Murdoch|1955|p=900}}{{sfn|Mountain|1957|p=610}} When the International Mineralogical Association was founded, bultfonteinite was grandfathered as a valid mineral species.<ref name=mindat/>

The type material is held in England at Cambridge University and the Natural History Museum in London.<ref name=handbook/>

==Occurrence== Bultfonteinite has been found in Australia, Botswana, Canada, Israel, Japan, Jordan, Russia, South Africa, and the United States.<ref name=mindat/> The mineral was first located outside South Africa in the US state of California in 1955.{{sfn|Murdoch|1955|p=900}} Bultfonteinite has been found in association with afwillite, apophyllite, calcite, natrolite, oyelite, scawtite, and xonotlite.<ref name=handbook/>

At the type locality, the mineral occurred in a large structure of dolerite and shale fragments in a kimberlite pipe.{{sfn|Parry|Williams|Wright|1932|p=145}} In Crestmore, California, bultfonteinite formed in the contact zone of thermally metamorphosed limestone.<ref name=handbook/>

==References== {{Reflist}}

'''Bibliography''' * {{Cite journal |last=McIver |first=E. J. |title=The structure of bultfonteinite, Ca<sub>4</sub>Si<sub>2</sub>O<sub>10</sub>F<sub>2</sub>H<sub>6</sub> |journal=Acta Crystallographica |year=1963 |volume=16 |issue=6 |pages=551–558 |doi=10.1107/S0365110X63001456 |url=http://journals.iucr.org/q/issues/1963/06/00/a03852/a03852.pdf |doi-access=free |bibcode=1963AcCry..16..551M |url-access=subscription}} * {{Cite journal |last=Mountain |first=E. D. |title=Rhodesite, a new mineral from the Bultfontein mine, Kimberley |journal=Mineralogical Magazine |date=December 1957 |volume=31 |issue=239 |pages=607–610 |url=http://www.minersoc.org/pages/Archive-MM/Volume_31/31-239-607.pdf |archive-url=https://web.archive.org/web/20170809233105/http://www.minersoc.org/pages/Archive-MM/Volume_31/31-239-607.pdf |archive-date=2017-08-09 |doi=10.1180/minmag.1957.31.239.01 |bibcode=1957MinM...31..607M}} * {{Cite journal |last=Murdoch |first=Joseph |title=Bultfonteinite from Crestmore, California |journal=American Mineralogist |date=September–October 1955 |volume=40 |issue=9 & 10 |pages=900–904 |url=http://www.minsocam.org/ammin/AM40/AM40_900.pdf |publisher=Mineralogical Society of America}} * {{Cite journal |last1=Parry |first1=John |last2=Williams |first2=Alpiieus F. |last3=Wright |first3=F. E. |title=On bultfonteinite, a new fluorine-bearing hydrouscalcium silicate from South Africa. |journal=Mineralogical Magazine |date=September 1932 |volume=23 |issue=138 |pages=145–162 |doi=10.1180/minmag.1932.023.138.01 |bibcode=1932MinM...23..145P |url=https://www.minersoc.org/pages/Archive-MM/Volume_23/23-138-145.pdf |archive-url=https://web.archive.org/web/20170815113957/https://www.minersoc.org/pages/Archive-MM/Volume_23/23-138-145.pdf |archive-date=2017-08-15}}

==External links== * {{Commonscat-inline|Bultfonteinite}}

Category:Calcium minerals Category:Crestmore Heights, California Category:Fluorine minerals Category:Minerals in space group 2 Category:Nesosilicates Category:Triclinic minerals