Alluaivite

Alluaivite is a rare mineral of the eudialyte group,[2] with complex formula written as Na19(Ca,Mn)6(Ti,Nb)3Si26O74Cl·2H2O.[3][2] It is unique among the eudialyte group as the only titanosilicate (other representatives of the group are usually zirconosilicates). The two dual-nature minerals of the group, being both titano- and zirconosilicates, are labyrinthite and dualite. They both contain alluaivite module in their structures.[4][5] Alluaivite is named after Mt. Alluaiv in Lovozero Tundry massif, Kola Peninsula, Russia, where it is found in ultra-agpaitic, hyperalkaline pegmatites.[1][2][3]

Alluaivite
General
CategorySilicate mineral, Cyclosilicate
Formula
(repeating unit)		Na19(Ca,Mn)6(Ti,Nb)3Si26O74Cl·2H2O
Strunz classification9.CO.10 (10 ed)
8/E.25-40 (8 ed)
Dana classification64.1b.1.1
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (3 2/m)
Space groupR3m
Unit cella = 14.04, c = 60.6 [Å]; Z = 6
Identification
ColorColorless to weak brownish pink
Crystal habitirregular accumulations
CleavageNone
FractureConchoidal
TenacityBrittle
Mohs scale hardness5-6
LusterVitreous
StreakWhite
DiaphaneityTransparent
Density2.76 (measured)
Optical propertiesUniaxial (+)
Refractive indexnω=1.62, nε=1.63 (approximated)
PleochroismColorless to pink (W), pink (E)
Ultraviolet fluorescenceOrange-red
Common impuritiesSr, REE, K, Ba, Zr
References[1][2]

Notes on chemistry

Alluaivite contains relatively high amounts of admixing strontium, cerium, potassium, and barium, with lesser amounts of substituting lanthanum and zirconium.[1]

Occurrence and association

Alluaivite was found in ultra-agpaitic (highly alkaline) pegmatites on Mt. Alluaiv, Lovozero massif, Kola Peninsula, Russia - hence its name. Associating minerals are aegirine, arfvedsonite, eudialyte, nepheline, potassic feldspar, and sodalite.[1]

References
  1. http://www.handbookofmineralogy.org/pdfs/Alluaivite.PDF Handbook of Mineralogy
  2. http://www.mindat.org/show.php?id=141&ld=2 Mindat
  3. Khomyakov A. P., Netschelyustov G. N. and Rastsvetaeva R. K. 1990: Alluaivite Na19(Ca,Mn)6(Ti,Nb)3Si26O74Cl.2H2O - A new titanosilicate mineral of eudialyte-like structure. Zapiski Vsesoyuznogo Mineralogicheskogo Obshchestva, 119(3), 117-120, in Jambor J. L. and Puziewicz J. 1991: New mineral names. American Mineralogist, 76, 1728-1735;
  4. Khomyakov, A.P., Nechelyustov, G.N., and Rastsvetaeva, R.K., 2006. Labyrinthite (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
  5. Khomyakov, A.P., Nechelyustov, G.N., and Rastsvetaeva, R.K., 2009: Dualite, 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


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