Ekplexite
A unique niobium sulfide-hydroxide — remarkable because niobium almost always appears in oxides, not sulfides.
Intro adapted from Wikipedia (CC BY-SA).
Ekplexite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula (Nb,Mo)S₂·(Mg₁₋ₓAlₓ)(OH)₂₊ₓ.
It crystallizes in the hexagonal crystal system. It is a member of the Valleriite structural group.
Key properties: Mohs hardness 1; specific gravity 3.63; Black streak; Metallic. Anisotropism: Strong luster.
IMA symbol Ekp, IMA status: approved, named in 2011.
Of hydrothermal origin in fenites formed by a peralkaline fluid, as a source of Nb, reacting with a large xenolith of alumina-rich metamorphic rocks (metapelites) in agpaitic nepheline syenite.
It is found associated with Orthoclase, anorthoclase, nepheline, fluorophlogopite, corundum, pyrrhotite, pyrite, rutile, monazite-(Ce), graphite, edgarite, molybdenite, tungstenite.
The name commemorates the Greek word έκπληξη with the meaning “surprise”, for its exotic combination of major chemical constituents.