Feklichevite
Mineral of the eudialyte group
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Feklichevite is a rare mineral of the eudialyte group with the formula Na11Ca9(Fe3+,Fe2+)2Zr3NbSi(Si3O9)2(Si9O27)2.[3][2] 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.[4] When compared to other minerals of the group, feklichevite characterizes in the presence of ferric iron (thus similar to ikranite, mogovidite and fengchengite[2]) and dominance of calcium at the N4 site. Calcium is ordered in the structure and is also present at the M1 site.[3][4] Other iron-bearing minerals of the group are eudialyte, ferrokentbrooksite, georgbarsanovite, khomyakovite, labyrinthite, oneillite and rastsvetaevite, but they rather contain ferrous iron[2] Feklichevite name honors Russian mineralogist and crystallographer, V. G. Feklichev.[3]
| Feklichevite | |
|---|---|
| General | |
| Category | Cyclosilicate |
| Formula | Na11Ca9(Fe3+,Fe2+)2Zr3Nb[Si25O73](OH,H2O,Cl,O)5 (original form) |
| IMA symbol | Fek[1] |
| Strunz classification | 9.CO.10 |
| Dana classification | 64.1.7. |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) 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 | [2][3] |
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 pyrrhotite.[3]
