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Ekplexite
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Ekplexite is a unique sulfide-hydroxide niobium-rich mineral with the formula (Nb,Mo)S2•(Mg1−xAlx)(OH)2+x.[5][3] 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".[5][3] 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.[6] 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.[7][3]
 | This article may be too technical for most readers to understand. (March 2016) |
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Notes on chemistry
Beside niobium, molybdenum, sulfur, magnesium and aluminium ekplexite contains also relatively small amounts of tungsten, vanadium and iron.[5]
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).[5]
Crystal structure
Crystal structure of ekplexite is described as non-commensurate. It is composed of two modules:[5]
- MeS2 sulfide module
- brucite-like (hydroxide) module
References
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