Fluorellestadite

{{short description|Nesosilicate mineral}} {{Infobox mineral | name = Fluorellestadite | category = Nesosilicates <br />Apatite structural group | image = Ellestadite-(F)-Calcite-215134.jpg | imagesize = 260px | caption = Fluorellestadite on blue calcite from the Crestmore Quarries, California, US | formula = Ca₁₀(SiO₄)₃(SO₄)₃F₂<ref name=IMA>[https://rruff.info/ima IMA Mineral List with Database of Mineral Properties]. Rruff.info. Retrieved on 2011-06-22.</ref> | IMAsymbol = Fel<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 = 503.55 g/mol | strunz = 9.AH.25 (10 ed) <br/><small>8/B.27-10 (8 ed)</small> | dana = 52.04.09.03 | system = Hexagonal | class = Dipyramidal (6/m) <br/>H-M symbol: (6/m) | symmetry = ''P''6₃/m | color = Light red, yellow, bluish green or colorless | habit = Acicular or hexagonal prismatic crystals, and fine-grained aggregates | twinning = | cleavage = Imperfect on {0001} | fracture = Conchoidal | tenacity = Very brittle | mohs = {{frac|4|1|2}} | luster = Sub-resinous to vitreous<ref name=AJS>Eakle and Rogers (1914) American Journal of Science 37: 262–267 (as Wilkeite)</ref> | refractive = n_ω = 1.638(2), n_ε = 1.632(2);<ref name = AM74/><br/> n_ω = 1.655, n_ε = 1.650<ref name=AM22/> | opticalprop = Uniaxial (-) | birefringence = | pleochroism = | streak = White with a weak bluish tint | gravity = 3.03 to 3.07 | melt = | fusibility = | diagnostic = | solubility = Easily soluble in dilute hydrochloric and nitric acids<ref name=AJS/> | diaphaneity = Transparent to translucent | other = Sometimes fluorescent. Not radioactive. | references = <ref name=Dana>Richard V. Gaines (1997) Dana’s New Mineralogy 8th ed. Wiley {{ISBN|0-471-19310-0}}</ref><ref name=Mindat>[http://www.mindat.org/min-1575.html Fluorellestadite: Fluorellestadite mineral information and data]. Mindat.org (2011-06-18). Retrieved on 2011-06-22.</ref><ref name=Webmin>[https://webmineral.com/data/Ellestadite-(F).shtml Ellestadite-(F) Mineral Data]. Webmineral.com. Retrieved on 2011-06-22.</ref><ref name=HOM>[https://rruff.geo.arizona.edu/doclib/hom/fluorellestadite.pdf Handbook of Mineralogy]. Handbook of Mineralogy. Retrieved on 2011-06-22.</ref> }}

'''Fluorellestadite''' is a rare nesosilicate of calcium, with sulfate and fluorine, with the chemical formula Ca₁₀(SiO₄)₃(SO₄)₃F₂.<ref name=IMA/> It is a member of the apatite group, and forms a series with hydroxylellestadite.

== Etymology == The mineral was originally named '''wilkeite''' by Eakle and Rogers in 1914, in honor of R. M. Wilke, a mineral collector and dealer.<ref name=AJS/> In 1922, a sample of “wilkeite” was analysed and found to be sufficiently different from the material reported by Eakle and Rogers to consider it a new species.<ref name=AM22>Duncan McConnell (1937) [http://www.minsocam.org/ammin/AM22/AM22_977.pdf The substitution of SiO4 – and SO4 – groups for PO4 -groups in the apatite structure; ellestadite, the end member] American Mineralogist 22: 977–986</ref> The name “ellestadite” was proposed, in honor of Reuben B Ellestad (1900–1993), an American analytic chemist from the Laboratory for Rock Analysis, University of Minnesota, US.<ref name=AM22/>

In 1982 Rouse and Dunn showed that the Si:S ratio was close to 1:1, giving the formula Ca₁₀(SiO₄)₃(SO₄)₃X₂, where X represents fluorine (F), hydroxyl (OH) or chlorine (Cl), and they named minerals in this group the ellestadite group.<ref name=AM67>Roland C. Rouse and Pete J. Dunn (1982) [http://www.minsocam.org/ammin/AM67/AM67_90.pdf A contribution to the crystal chemistry of ellestadite and the silicate sulfate apatites] American Mineraleralogist 67: 90–96</ref> The end members of the group were named hydroxylellestadite (X = OH), fluorellestadite (X = F) and chlorellestadite (X = Cl); ideal end-member chlorellestadite is assumed not to exist in nature, although it has been synthesized.<ref name=Mindat/> Wilkeite was discredited as a unique species, as it is not an end member of any solid solution series, but an intermediate member.<ref name=AM67/>

The name fluorellestadite was changed to ellestadite-(F) in 2008<ref name=Minrec>Burke (2008) The Mineralogical Record 39: 131</ref> and changed back to fluorellestadite in 2010.<ref name=EJM>{{cite journal|journal=European Journal of Mineralogy|doi=10.1127/0935-1221/2010/0022-2022|title=Nomenclature of the apatite supergroup minerals|year=2010|last1=Pasero|first1=Marco|last2=Kampf|first2=Anthony R.|last3=Ferraris|first3=Cristiano|last4=Pekov|first4=Igor V.|last5=Rakovan|first5=John|last6=White|first6=Timothy J.|volume=22|issue=2|pages=163–179|bibcode=2010EJMin..22..163P}}</ref>

== Structure == The ellestadites are nesosilicates, which are minerals with isolated SiO₄ tetrahedra. They are members of the apatite group, but whereas phosphorus is one of the chief constituents of apatite, in ellestadite it is almost completely replaced by sulfur and silicon, without appreciably altering the structure.<ref name=AM22/> The crystal class is hexagonal 6/m, space group P6₃/m. The tetrahedral groups are arranged to create the 6₃ screw axis, and the fluorine atoms are located in channels parallel to this direction.<ref name=Dana/> Some sources give unit cell parameters for one formula unit per unit cell (Z = 1), but some scientists consider the formula to be half the value accepted by the International Mineralogical Association (IMA), i.e. Ca₅((Si,S)O₄))₃F, with two formula units per unit cell (Z = 2). Cell parameters for natural, as opposed to synthetic, material are a = 9.41 to 9.53 Å, and c = 6.90 to 6.94 Å. Rouse and Dunn postulated a hypothetical pure end-member with a = 9.543 Å and c = 6.917 Å.<ref name=AM67/> Synthetic material has a = 9.53 to 9.561 Å, and c = 6.91 to 6.920 Å.<ref name=Dana/>

== Appearance == Fluorellestadite occurs as acicular or hexagonal prismatic, poorly terminated crystals, and as fine-grained aggregates.<ref name=AM74>John J. Jambor and Jacek Puziewicz (1989) [http://www.minsocam.org/ammin/AM74/AM74_500.pdf New Mineral Names] American Mineralogist 74: 500, abstract of Chesnokov, Bazhenova and Bushmakin (1987) Zapiski Vses. Mineralog, Obshch 116:743 (in Russian) </ref><ref name=HOM/> Crystals are transparent and aggregates are translucent.<ref name=AM74/> Material from Crestmore, California, is light rose-red or yellow in color,<ref name=AJS/><ref name=Dana/><ref name=Mindat/> and typically occurs in a matrix of blue calcite. Material from Russia is pale bluish-green or colorless.<ref name=AM74/><ref name=HOM/> The streak is white with a weak bluish tint, and the luster is sub-resinous on broken surfaces, but very brilliant on prism faces.<ref name=AJS/>

== Physical properties == Fluorellestadite shows imperfect cleavage perpendicular to the long crystal axis.<ref name=AJS/><ref name=Mindat/> The mineral is very brittle, and breaks with a conchoidal fracture.<ref name=AM74/> Its hardness is {{frac|4|1|2}}, between that of fluorite and apatite, and its specific gravity is 3.03 to 3.07, similar to that of fluorite. It is easily soluble in dilute hydrochloric and nitric acids<ref name=AJS/> and is not radioactive.<ref name=Webmin/> When intensely heated, ellestadite (wilkeite) becomes colorless and then assumes a pale bluish green color on cooling.<ref name=AJS/>

The mineral is uniaxial (-), with refractive indices n_ω = 1.638 to 1.655 and n_ε = 1.632 to 1.650.<ref name=AM74/><ref name=AM22/> It is sometimes fluorescent, white to blue-white or yellow-white in short-wave ultraviolet light, and medium white-yellow-brown or weak white in long-wave light.<ref name=Dana/><ref name=Webmin/>

== Occurrence and associations == The type locality is Coal Mine No. 44, Kopeisk, Chelyabinsk coal basin, Chelyabinsk Oblast, Southern Urals, Russia,<ref name=Mindat/> and type material is held at the Fersman Mineralogical Museum, Academy of Sciences, Moscow, Russia.<ref name=AM74/> Ellestadite is a skarn mineral. It occurs associated with diopside, wollastonite, idocrase, monticellite, okenite, vesuvianite, calcite and others at Crestmore, Riverside County, California, US.<ref name=AM22/><ref name=Dana/> At Crestmore a contact zone exists between crystalline limestone and granodiorite. The area was quarried for limestone in the early 1900s, revealing varied associations of metamorphic minerals, including ellestadite (named as wilkeite) with garnet, vesuvianite and diopside, in blue calcite.<ref name=AJS/> At the type locality it was formed in burned fragments of petrified wood in coal dumps, associated with lime, periclase, magnesioferrite, hematite, srebrodolskite and anhydrite.<ref name=AM74/><ref name=HOM/> Ellestadite (wilkeite) is often altered to okenite.<ref name=AJS/>

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

== External links == *[https://rruff.geo.arizona.edu/AMS/viewJmol.php?id=16819 JMol] {{Commons category|position=left}}

<!--- Categories ---> Category:Calcium minerals Category:Nesosilicates Category:Crestmore Heights, California Category:Hexagonal minerals Category:Minerals in space group 176