Ekplexite
 | This article may be too technical for most readers to understand. (March 2016) |
| Ekplexite | |
|---|---|
| General | |
| Category | Sulfide mineral |
| Formula (repeating unit) | (Nb,Mo)S2•(Mg1−xAlx)(OH)2+x |
| Crystal system | Trigonal |
| Crystal class | 3m, 32 or 3m |
| Space group | P321, P3m1, P3m1 |
| Unit cell | a = 3.79, c = 11.3 [Å] (approximated) Z = 2 |
| Identification | |
| Color | Iron-black |
| Crystal habit | micaceous flakes (may be arranged in chaotic or radiating aggregates), in lenticular nests |
| Cleavage | {001}, perfect |
| Tenacity | Flexible |
| Mohs scale hardness | 1 |
| Luster | Metallic |
| Diaphaneity | Opaque |
| Density | 3.63 |
| Pleochroism | light gray to dark gray (strong) |
| Common impurities | W, V, Fe |
| References | [1][2][3] |
Ekplexite is a unique sulfide-hydroxide niobium-rich mineral with the formula (Nb,Mo)S2•(Mg1−xAlx)(OH)2+x.[4][2] It is unique because niobium is usually found in oxide or, eventually, silicate minerals. Ekplexite is a case in which chalcophile behaviour of niobium is shown, which means niobium present in a sulfide mineral. The unique combination of elements in ekplexite has to do with its name, which comes from a Greek world on "surprise".[4][2] The other example of chalcophile behaviour of niobium is edgarite, FeNb3S6, and both minerals were found in the same environment, which is a fenitic rock of Mt. Kaskasnyunchorr, Khibiny Massif, Kola Peninsula, Russia.[5] Analysis of the same rock has revealed the presence of two analogues of ekplexite, kaskasite (molybdenum-analogue) and manganokaskasite (molybdenum- and manganese-analogue). All three minerals belong to the valleriite group, and crystallize in the trigonal system with similar possible space groups.[6][2]
Notes on chemistry
Beside niobium, molybdenum, sulfur, magnesium and aluminium ekplexite contains also relatively small amounts of tungsten, vanadium and iron.[4]
Association and environment
The rock in which contains ekplexite is classified as fenite. In this rock ekplexite associates with fluorophlogopite, nepheline, orthoclase-anorthoclasee (silicates), alabandine, edgarite, pyrite, molybdenite, tungstenite (sulfides), corundum, graphite and monazite-(Ce).[4]
Crystal structure
Crystal structure of ekplexite is described as non-commensurate. It is composed of two modules:[4]
- MeS2 sulfide module
- brucite-like (hydroxide) module
References
- ^ Pekov., I.V., Yapaskurt, V.O., Polekhovsky, Y.S., Vigasina, M.F., and Siidra, O.I., 2014. Ekplexite (Nb,Mo)S2·(Mg1−xAlx)(OH)2+x, kaskasite (Mo,Nb)S2·(Mg1−xAlx)(OH)2+x and manganokaskasite (Mo,Nb)S2·(Mn1−xAlx)(OH)2+x, three new valleriite-group mineral species from the Khibiny alkaline complex, Kola peninsula, Russia. Mineralogical Magazine 78(3), 663-679.
- ^ a b c d "Ekplexite: Ekplexite mineral information and data". Mindat.org. Retrieved 2016-03-04.
- ^ "Ekplexite - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-10.
- ^ a b c d e Pekov., I.V., Yapaskurt, V.O., Polekhovsky, Y.S., Vigasina, M.F., and Siidra, O.I., 2014. Ekplexite (Nb,Mo)S2·(Mg1−xAlx)(OH)2+x, kaskasite (Mo,Nb)S2·(Mg1−xAlx)(OH)2+x and manganokaskasite (Mo,Nb)S2·(Mn1−xAlx)(OH)2+x, three new valleriite-group mineral species from the Khibiny alkaline complex, Kola peninsula, Russia. Mineralogical Magazine 78(3), 663-679.
- ^ "Edgarite: Edgarite mineral information and data". Mindat.org. Retrieved 2016-03-04.
- ^ Pekov., I.V., Yapaskurt, V.O., Polekhovsky, Y.S., Vigasina, M.F., and Siidra, O.I., 2014. Ekplexite (Nb,Mo)S2·(Mg1−xAlx)(OH)2+x, kaskasite (Mo,Nb)S2·(Mg1−xAlx)(OH)2+x and manganokaskasite (Mo,Nb)S2·(Mn1−xAlx)(OH)2+x, three new valleriite-group mineral species from the Khibiny alkaline complex, Kola peninsula, Russia. Mineralogical Magazine 78(3), 663-679
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