Cyrilovite

{{Short description|Hydrous sodium iron phosphate mineral}} {{Infobox mineral | name = Cyrilovite | category = Phosphate mineral | image = Cyrilovite-141091.jpg | imagesize = 260px | alt = | caption = | formula = NaFe3+3(PO4)2(OH)4·2(H2O) | IMAsymbol = Cyr<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 = 8.DL.10 | dana = 42.07.08.01 | system = Tetragonal | class = Trapezohedral (422) H–M symbol: (422) | symmetry = ''P''41212 | color = Bright yellow, honey-yellow, orange to brownish yellow, brown | colour = | habit = Massive, granular, pseudo cubic, radiating to botryoidal aggregates and crusts | twinning = | cleavage = None | fracture = Conchoidal | tenacity = | mohs = 4 | luster = Vitreous | streak = Yellow | diaphaneity = Translucent | gravity = 3.081–3.096 | density = | polish = | opticalprop = Uniaxial (-) | refractive = ''n''ω = 1.802–1.805, ''n''ε = 1.769–1.775 | birefringence = δ = 0.033 | pleochroism = Weak | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = <ref name=Handbook/><ref name=Mindat/><ref name=Webmin>https://webmineral.com/data/Cyrilovite.shtml Webmineral data</ref><ref>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Cyrilovite Mineralienatlas]</ref> }} '''Cyrilovite''' (NaFe33+(PO4)2(OH)4·2(H2O)) is a hydrous sodium iron phosphate mineral. It is isomorphous and isostructural with wardite, the sodium aluminium counterpart.<ref name=Lindberg>Lindberg, M. L. (1957) Relationship of the minerals avelinoite, cyrilovite, and wardite. American Mineralogist, 42, 204–213.</ref>

Cyrilovite is found in granitic pegmatites.<ref name=Fransolet>Fransolet, A. M., Cooper, M. A., Cerny, P., Hawthorne, C., Chapman, R. (2000) The tanco pegmatite at Bernic Lake, Southeastern Manitoba. The Canadian Mineralogist, 38, 893–898.</ref> It was first discovered in 1953 in a pegmatite at Cyrilov, near Velké Meźiřiči, West Moravia, Czech Republic.<ref name=Mindat>http://www.mindat.org/min-1206.html Mindat.org.</ref>

== Composition ==

The chemical formula of cyrilovite is NaFe3+3(PO4)2(OH)4·2(H2O).<ref name=Handbook>https://rruff.geo.arizona.edu/doclib/hom/cyrilovite.pdf Handbook of Mineralogy</ref> Parent phosphate minerals, fluorapatite and triplite-zwieselite, were transformed by hydrothermal alteration and weathering to give a complex, microcrystalline intergrowth of secondary phosphate minerals that include cyrilovite.<ref name=Lottermoser>Lottermoser, B., Lu, J. (1997) Petrogenesis of rare-element pegmatites in the Olary Block, South Australia. 1. Mineralogy and chemical evolution. Mineralogy & Petrology, 59, 1–19.</ref> The sequence of phosphate transformations ended with the formation of cyrilovite within the fluorapatite fractures and the replacement of fluorapatite by lipscombite and crandallite-group minerals.<ref name=Lottermoser/> Fransolet suggest that a part of the leached Na leads to the precipitation of cyrilovite, in the fissures cause by the volume decrease resulting from the transformation of typhylite to heteresoite.<ref name=Fransolet/> Mobilization of alkalis and of relatively immobile elements including aluminium and rare-earth elements are subsequently incorporated into precipitating cyrilovite, lipscombite and crandallite-group minerals.<ref name=Lottermoser/> The chemical analysis shows substitution not only of Al for Fe, but also of K and Mn for Na, measured and observed specific gravities are considered to be in good agreement.<ref name=Lindberg/> Ferric iron occurs virtually alone in H2O rich minerals such as phosphosiderite, and coupled with Na, K, or Ca in cyrilovite.<ref name=Fransolet/> It is soluble in hot dilute HCl, in hot dilute H2SO4, and, with difficulty, in hot dilute HNO3.<ref name=Lindberg/> In the closed tube, it gives off water and fuses.<ref name=Lindberg/>

==Geologic occurrence==

The mineral wardite is capable of crystallizing in a similar form to that of cyrilovite because of their closely related chemical compositions. Between wardite's composition, NaAl3(PO4)2(OH)4·2(H2O), and cyrilovite's composition, NaFe3(PO4)2(OH)4·2(H2O), they are able to form end members of a series of solid solutions. Either of the two minerals can occur in various proportions in a series of solid solutions in the wardite mineral group. Cyrilovite is a rare accessory mineral in some oxidizing phosphate-bearing granite pegmatitles and iron deposits. The sequence of phosphate transformations ended with the formation of cyrilovite within the F-apatite factures and the replacement of F-apatite by lipscombite and crandillite-group minerals.<ref name=Lottermoser/> Weathering-related cyrilovite, lipscombite, and crandillite-group minerals were formed by percolating meteoric waters under increasing oxygen fugacity.<ref name=Lottermoser/>

==Structure==

The crystal structures of natural wardite and of the isomorphous cyrilovite have the space group P41212, Z=4). Hydrogen atoms were not located, but reasonable positions can be estimated. The cell dimensions of cyrilovite are: ''c'' = 19.4, ''a'' = 7.32 Å.<ref name=Lindberg/> The individual crystals are usually smaller than 0.1 mm and many of them are intergrown. Crystals are squat and when single tend to lie on the basal pinacoid. The pinacoid {001} and the dipyramid {113} are the dominant forms; all the faces of these forms tend to be present and equally well developed. The dipyramid {012} is not always present. The direction for the a-axis is at 45° angle to the smallest primitive unit cell.<ref name=Lindberg/>

== Physical properties ==

Cyrilovite is a vitreous translucent mineral that can appear in colors ranging from a bright yellow, honey-yellow, orange to brownish yellow, or brown and it has a hardness of 4. It has a yellow streak. The mineral is classified under the space group P41212 and is tetragonal.<ref name=Handbook/>

== References == {{Reflist}} *Breitinger, D. K., et al. (2004) Combined vibrational spectra of natural wardite. Journal of Molecular Structure, 706, 95–99. *Cooper, M., Hawthorne, F. C., Cerny, P. (2000) Refinement of the crystal structure of cyrilovite from cyrilov, western Moravia, Czech Republic. Journal of Czech Geological Society, 45, 95–100.

Category:Sodium minerals Category:Iron(III) minerals Category:Phosphate minerals