Voronkovite

Voronkovite is a very rare mineral[1] of the eudialyte group with the formula Na15(Na,Ca,Ce)3(Mn,Ca)3Fe3Zr3Si2Si24O72(OH,O)4Cl·H2O.[2] The formula is based on the simplified original one; it does not show the presence of cyclic silicate groups, but two M3- and M4-site silicon atoms are shown separately (basing on the nomenclature of the eudialyte group[3]). Voronkovite has lowered symmetry (space group R3, instead of more specific for the group R3m one), similarly to some other eudialyte-group members: aqualite, labyrinthite, oneillite and raslakite.[1] The specific feature of voronkovite is, among others, strong enrichment in sodium.[2]

Voronkovite
General
CategorySilicate mineral, Cyclosilicate
Formula
(repeating unit)		Na15(Na,Ca,Ce)3(Mn,Ca)3Fe3Zr3
Si26O72(OH,O)4Cl·H2O (original form)
Strunz classification9.CO.10
Crystal systemTrigonal
Crystal classPyramidal (3)
H-M symbol: (3)
Space groupR3
Unit cella = 14.21, c = 30.27 [Å]; Z = 3
Identification
ColorLight brown
Crystal habitRounded crystals
FractureConchoidal
TenacityBrittle
Mohs scale hardness5
LusterVitreous
StreakWhite
DiaphaneityTransparent
Density2.95 g/cm3 (calculated)
Optical propertiesUniaxial (+)
PleochroismLemon yellow (X), brownish pink (Y)
References[1][2]

Occurrence and association

Voronkovite comes from an ultra-alkaline pegmatite of Mt. Alluaiv, Lovozero massif, Kola Peninsula, Russia. It associates with aegirine, lomonosovite, manganoneptunite, microcline, nepheline, shkatulkalite, sodalite, terskite, sphalerite and vuonnemite.[2]

Notes on chemistry

Voronkovite has additional impurities, not given in the formula. They include strontium, fluorine, potassium, lanthanum, neodymium (at the Mn site), niobium, and minor hafnium and aluminium.[2]

References
  1. Mindat, Voronkovite, http://www.mindat.org/min-32199.html
  2. Khomyakov, A.P., Nechelyustov, G.N., and Rastsvetaeva, R.K., 2010, Voronkovite, Na15(Na,Ca,Ce)3(Mn,Ca)3Fe3Zr3Si26O72(OH,O)4Cl·H2O, a new mineral species of the eudialyte group from the Lovozero alkaline pluton, Kola Peninsula, Russia. Geology of Ore Deposits 51(8), 750-756
  3. 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


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