Voronkovite

Voronkovite
General
Category Silicate mineral, Cyclosilicate
Formula
(repeating unit)		 Na15(Na,Ca,Ce)3(Mn,Ca)3Fe3Zr3Si26O72(OH,O)4Cl·H2O (original form)
Strunz classification 9.CO.10
Crystal system Trigonal
Unit cell a=14.21, c=30.27 [Å]; Z = 3
Identification
Color Light brown
Crystal habit Rounded crystals
Crystal symmetry Trigonal - pyramidal
Point group 3
Space group R3
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 5
Luster Vitreous
Streak White
Diaphaneity Transparent
Density 2.95 g/cm3 (calculated)
Optical properties Uniaxial (+)
Pleochroism Lemon yellow (X), brownish pink (Y)
References [1][2]

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]

Occurrence and association

Voronkovite comes form 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. 1 2 3 Mindat, Voronkovite, http://www.mindat.org/min-32199.html
  2. 1 2 3 4 5 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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