Feklichevite
Feklichevite | |
---|---|
General | |
Category | Cyclosilicate |
Formula (repeating unit) | Na11Ca9(Fe3+,Fe2+)2Zr3Nb[Si25O73](OH,H2O,Cl,O)5 (original form) |
Strunz classification | 9.CO.10 |
Dana classification | 64.1.7. |
Crystal system | Trigonal Ditrigonal pyramidal class |
Space group | Trigonal H-M symbol: (3m) Space group: R3m |
Unit cell | a = 14.26, c = 30.17 [Å] (approximated); Z = 3 |
Identification | |
Color | Dark brown |
Crystal habit | isometric, thick-tabular; grains |
Cleavage | (001), perfect |
Tenacity | Brittle |
Mohs scale hardness | 5.5 |
Luster | Vitreous |
Streak | Brownish |
Diaphaneity | Transparent or Translucent |
Density | 2.87 (approximated) |
Optical properties | Uniaxial (+) |
Refractive index | nω=1.61, nε=1.61 (approximated) |
Pleochroism | None |
Ultraviolet fluorescence | No |
Common impurities | Mn, F |
References | [1][2] |
Feklichevite is a rare mineral of the eudialyte group with the formula Na11Ca9(Fe3+,Fe2+)2Zr3NbSi(Si3O9)2(Si9O27)2.[2][1] The original formula was extended to show the presence of cyclic silicate groups and presence of silicon at the M4 site, according to the nomenclature of eudialyte group.[3] When compared to other minerals of the group, feklichevite characterizes in the presence of ferric iron (thus similar to ikranite, mogovidite and fengchengite[1]) and dominance of calcium at the N4 site. Calcium is ordered in the structure and is also present at the M1 site.[2][3] Other iron-bearing minerals of the group are eudialyte, ferrokentbrooksite, georgbarsanovite, khomyakovite, labyrinthite, oneillite and rastsvetaevite, but they rather contain ferrous iron[1] Feklichevite name honors Russian mineralogist and crystallographer, V. G. Feklichev.[2]
Occurrence and association
Feklichevite was found in cancrinite syenite vein of pegmatoid type, that occurs in the Kovdor alkaline massif, Kola Peninsula, Russia. Feklichevite coexists with aegirine-diopside, cancrinite, potassic feldspar, pectolite, titanite, hematite, and руrrhоtitе.[2]
Notes on chemistry
Feklichevite has quite high admixtures of manganese and fluorine, with minor hafnium, strontium, titanium, cerium, and lanthanum.[2]
References
- ^ a b c d Mindat, Feklichevite, http://www.mindat.org/min-11029.html
- ^ a b c d e f Pekov, I.V., Ekimenkova, I.A., Chukanov, N.V., Rastsvetaeva, R.K., Kononkova, N.N., Pekova, N.A., and Zadov, A.E., 2001. Feklichevite Na11Ca9(Fe3+,Fe2+)2Zr3Nb[Si25O73](OH,H2O,Cl,O)5, a new mineral of the eudialyte group from Kovdor Massif, Kola peninsula. Zapiski Vserossijskogo Mineralogicheskogo Obshchestva 130(3), 55-65
- ^ a b 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