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columbite


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A mineral oxide (Fe,Mn)(Ta,Nb)2O6; when Ta > Nb the mineral is called tantalite, but when Ta < Nb it is called columbite; sp. gr. 5.2–6.5, increasing with increasing Ta content; hardness 6.0–6.5; orthorhombic; weakly magnetic; black or brownish-black; very dark red streak; sub-metallic lustre; crystals normally tabular and short prismatic forms, and can also be blade-like; cleavage pinacoidal; occurs in granites and pegmatites in association with high-temperature minerals, e.g. cassiterite, wolframite, tourmaline, quartz, and feldspar. It is a major ore mineral of niobium.

Subjects: Earth Sciences and Geography.


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