Tapiolite

Tapiolite [(Fe, Mn)(Nb, Ta)₂O₆] is a black mineral series that is an ore of niobium and tantalum. The tapiolite group includes tapiolite-(Fe) or ferrotapiolite and tapiolite-(Mn) or manganotapiolite.^[3][4][5] Tapiolite-(Fe) is by far the more common of the two.^[6][7]

Tapiolite
General
Category	Minerals
Formula	(Fe, Mn)(Nb, Ta)2O6
IMA symbol	Tap[1]
Crystal system	Tetragonal
Crystal class	Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m)
Space group	P42/mnm
Identification
References	[2]

The minerals have a submetallic luster and a high specific gravity with tapiolite-Fe having a higher specific gravity (7.90)^[6] versus 7.72 for tapiolite-Mn.^[7]

The mineral was named in 1863 after the forest god Tapio of Finnish mythology, and the original tapiolite material came from Sukula, Tammela, Tavastia Proper, Finland.^[3][8]

Tapiolite is very close to columbite and tantalite. Those minerals have the same chemical composition, but different crystal symmetry orthorhombic for tantalite or columbite and tetragonal for tapiolite.^[9]

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  Crystal structure of tapiolite