Nioboholtite
The niobium analogue of holtite — an extremely rare member of the dumortierite supergroup.
Intro adapted from Wikipedia (CC BY-SA).
Nioboholtite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Nb₀.₆ ₀.₄)Al₆BSi₃O₁₈.
It crystallizes in the orthorhombic crystal system (space group Pnma). It is a member of the Dumortierite structural group.
Key properties: specific gravity 3.72; White streak; optically biaxial.
IMA symbol Nhlt, IMA status: approved, named in 2012.
Found in the internal portion of a complex zoned granitic pegmatite.
It is found associated with Holtite, microcline, quartz, muscovite, spessartine, chrysoberyl, zircon, monazite-(Ce), cheralite, xenotime-(Y), Mn-rich fluor-, hydroxyl- and chlorapatite.
The name refers to the composition and the relationship to holtite.