{{Short description|Mineral of the eudialyte group}} {{More citations needed|date=September 2021}}{{infobox mineral | name = Labyrinthite | category = Silicate mineral, cyclosilicate | image = | imagesize = | alt = | caption = | formula = {{chem2|(Na,K,Sr)35Ca12Fe3Zr6TiSi51O144(O,OH,H2O)9Cl3}} | IMAsymbol = Lby<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> | strunz = | dana = | system = Trigonal | class = Pyramidal (3) <br/><small>(same H-M symbol)</small> | symmetry = ''R''3 | unit cell = a = 14.24, c = 60.73&nbsp;[Å] (approximated); Z&nbsp;=&nbsp;3 | color = Pink | colour = | habit = anhedral grains | twinning = | cleavage = None | fracture = Conchoidal | tenacity = Brittle | mohs = 5–6 | luster = Vitreous | streak = White | diaphaneity = Transparent | gravity = | density = 2.88 g/cm<sup>3</sup> (measured) | polish = | opticalprop = Uniaxial (+) | refractive = n<sub>0</sub> = 1.60, n<sub>e</sub> = 1.60 (approximated) | birefringence = | pleochroism = None | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = surface alteration to lovozerite, zirsinalite and thermonatrite | other = | references = <ref name=Mindat /><ref name=ZVMO /> }} '''Labyrinthite''' is a very rare mineral of the eudialyte group.<ref name=Mindat>Mindat, http://www.mindat.org/min-27420.html</ref> When compared to other species in the group, its structure is extremely complex – with over 100 sites and about 800 cations and anions – hence its name, with its complexity expressed in its chemical formula {{chem2|(Na,K,Sr)35Ca12Fe3Zr6TiSi51O144(O,OH,H2O)9Cl3}}.<ref name=Mindat /><ref name=ZVMO>Khomyakov, A.P., Nechelyustov, G.N., and Rastsvetaeva, R.K., 2006. Labyrinthite {{chem2|(Na,K,Sr)35Ca12Fe3Zr6TiSi51O144(O,OH,H2O)9Cl3}}, a new mineral with a modular eudialyte-like structure from Khibiny Alkaline Massif, Kola Peninsula, Russia. Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva 135(2), 38–49</ref> The formula is simplified as it does not show the presence of cyclic silicate groups. Complexity of the structure results in symmetry lowering (likely due to ordering of cations) from the typical centrosymmetrical group to ''R''3 space group.<ref name=ZVMO /> Other eudialyte-group representatives with such symmetry lowering include aqualite, oneillite, raslakite, voronkovite.<ref name=Mindat /> Labyrinthite is the second dual-nature (both zircono- and titanosilicate) representative of the group after dualite<ref>Khomyakov, A.P., Nechelyustov, G.N., and Rastsvetaeva, R.K., 2009: Dualite, {{chem2|Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3MnSi51O144(OH,H2O,Cl)9}}, a new zircono-titanosilicate with a modular eudialyte-like structure from the Lovozero alkaline Pluton, Kola Peninsula, Russia. Geology of Ore Deposits 50(7), 574–582</ref> and third with essential titanium after dualite and alluaivite.<ref name=Mindat />

==Occurrence and association== Labyrinthite was discovered in hyperagpaitic (ultra-alkaline) pegmatite at Mt. Nyorkpakhk, Khibiny massif, Kola Peninsula, Russia, where it represents a late-stage mineral. It coexists with aegirine, alkaline amphibole, lamprophyllite, lomonosovite, potassium feldspar, pectolite, sodalite, and villiaumite.<ref name=ZVMO></ref>

==Notes on chemistry== Beside that given in the formula, other elements substituting the main ones in labyrinthite are manganese, fluorine, and cerium.<ref name=ZVMO />

==Notes on crystal structure== Labyrinthite is two-modular – its structure contains alluaivite-like and eudialyte-like module. The framework of labyrinthite is 24-layered. It also characterize in doubled ''c'' unit cell parameter.<ref name=ZVMO />

==References== {{reflist}}

==Further reading== * Johnsen, O., Ferraris, G., Gault, R.A., Grice, D.G., Kampf, A.R., and Pekov, I.V., 2003. The nomenclature of eudialyte-group minerals. The Canadian Mineralogist 41, 785–794

Category:Cyclosilicates Category:Sodium minerals Category:Calcium minerals Category:Iron minerals Category:Zirconium minerals Category:Titanium minerals Category:Trigonal minerals Category:Minerals in space group 146

{{silicate-mineral-stub}}