Category Sulfide mineral Crystal class 3m, 32 or 3m | Crystal system Trigonal Space group P321, P3m1, P3m1 | |
Formula
(repeating unit) (Nb,Mo)S2·(Mg1−xAlx)(OH)2+x Unit cell a = 3.79, c = 11.3 [Å] (approximated)
Z = 2 | ||
Ekplexite is a unique sulfide-hydroxide niobium-rich mineral with the formula (Nb,Mo)S2•(Mg1−xAlx)(OH)2+x. 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". 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. 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.
Contents
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).
Crystal structure
Crystal structure of ekplexite is described as non-commensurate. It is composed of two modules: