Feklichevite
| Feklichevite | |
|---|---|
| General | |
| Category | Silicate mineral, Cyclosilicate |
| Formula (repeating unit) | Na11Ca9(Fe3+,Fe2+)2Zr3Nb[Si25O73](OH,H2O,Cl,O)5 (original form) |
| Dana classification | 64.1.7. |
| Crystal system | Trigonal, R3m' |
| Unit cell | a=14.26, c=30.17 [Å] (approximated) |
| Identification | |
| Color | Dark brown |
| Crystal habit | isometric, thick-tabular; grains |
| Crystal symmetry | Trigonal - Ditrigonal Pyramidal (3m) |
| 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
- 1 2 3 4 Mindat, Feklichevite, http://www.mindat.org/min-11029.html
- 1 2 3 4 5 6 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
- 1 2 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