Voronkovite
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Voronkovite is a very rare mineral[2] of the eudialyte group with the chemical formula Na15(Na,Ca,Ce)3(Mn,Ca)3Fe3Zr3Si2Si24O72(OH,O)4Cl·H2O.[3] 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[4]). 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.[2] The specific feature of voronkovite is, among others, strong enrichment in sodium.[3]
| Voronkovite | |
|---|---|
| General | |
| Category | Silicate mineral, Cyclosilicate |
| Formula | Na15(Na,Ca,Ce)3(Mn,Ca)3Fe3Zr3Si26O72(OH,O)4Cl·H2O (original form) |
| IMA symbol | Vrk[1] |
| Strunz classification | 9.CO.10 |
| Crystal system | Trigonal |
| Crystal class | Pyramidal (3) H-M symbol: (3) |
| Space group | R3 |
| Unit cell | a = 14.21, c = 30.27 [Å]; Z = 3 |
| Identification | |
| Color | Light brown |
| Crystal habit | Rounded crystals |
| 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 | [2][3] |
Occurrence and association
Voronkovite comes from an ultra-alkaline pegmatite of Mt. Alluaiv, Lovozero Massif, Kola Peninsula, Russia. It occurs with aegirine, lomonosovite, manganoneptunite, microcline, nepheline, shkatulkalite, sodalite, terskite, sphalerite and vuonnemite.[3]
