Niobium, formerly columbium, is a chemical element with the symbol Nb and atomic number 41. It is a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite. The name comes from Greek mythology: Niobe, daughter of Tantalus.
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Some articles on niobium:
... Niobium has no known biological role ... While niobium dust is an eye and skin irritant and a potential fire hazard, elemental niobium on a larger scale is physiologically inert (and thus ... Niobium-containing compounds are rarely encountered by most people, but some are toxic and should be treated with care ...