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Columbite-(Fe) with Montebrasite

#PD34521

Columbite-(Fe) with Montebrasite

#PD34521
Availability
Sold
Size
7 x 6 x 3.5 cm - Sm Cabinet 
Formula
Fe2+Nb2O6 (RRUFF)
Locality
Custer dist., Custer Co., South Dakota, United States

We do not have a specific locality for this specimen, however if I had to choose it would be Tin Mountain, which is rich in Montebrasite. the large, dull black Ferrocolumbite crystal attached to the Montebrasite shows a few good faces and is 4 x 4.5cm and is 1.3cm wide. The Black Hills are known for their zoned pegmatites and the "Columbite-Tantalite" series is found in most of them. Some of the more well-known mines include the Tin Mountain as well as the Etta, Nickel Plate, Ingersoll and Dan Patch. Historically, these have been lumped into the series 'Columbite-Tantalite' or "Col-Tan" and more properly called the Columbite-(Fe)-Tantalite-(Fe) series, which covers the range of compositions rich in Niobium(Nb) to Tantalum(Ta). It is impractical to test the composition of all of them, although I believe most are high in iron.

Columbite-(Fe)

Formula
Fe2+Nb2O6 
Crystal System
Orthorhombic 
Crystal Habit
Massive - Granular, Striated 
Cleavage
Distinct, None, None 
Luster
Sub Metallic 
Color
black, brownish black 
Streak
blackish brown 
Class
Orthorhombic - Dipyramidal 
Fracture
Sub Conchoidal 
Hardness

Data courtesy of Webmineral.

Collection
Phillips Collection

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