Ekplexite
# Ekplexite

Ekplexite is a unique sulfide-hydroxide niobium-rich mineral with the formula $(Nb,Mo)S_2•(Mg_{1−x}Al_x)(OH)_{2+x}.$ 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, $FeNb_3S_6,$ 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.

## Notes on chemistry

Beside niobium, molybdenum, sulfur, magnesium and aluminium ekplexite contains also relatively small amounts of tungsten, vanadium and iron.

## 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:

* $MeS_2$ sulfide module
* brucite-like (hydroxide) module
