Niobium crustal abundance

Impure tantalum was isolated in 1825 by Swiss chemist Jean-Charles-Galissard de Marignac and, in purer form, by Heinrich Rose in 1844. It is found, in combination with its congener niobium, in tantalite/columbite (Fe, Mn)(Ta, Nb)206 ore, with tantalite containing more tantalum than niobium. Its crustal abundance is 1.7 parts per million, with major deposits in Australia, Brazil, China, Africa, the former Soviet Union, and Canada. The ore is concentrated, refined to the oxide Ta205, converted to K2TaF7, and reduced to the metal. 

Elemental niobium has an approximate crustal abundance on the average of 20 mgkg, with a range of 0.32 to 24 mgkg, while soils contain a mean of... 

Rehnements of the Taylor and McLennan (1985) model are provided by McLennan and Taylor (1996) and McLennan (2001b). The latter is a modihcation of several trace-element abundances in the upper crust and as such, should not affect their compositional model for the bulk crust, which does not rely on their upper crustal composition. Nevertheless, McLennan (2001b) does provide modihed bulk-crust estimates for niobium, rubidium, caesium, and tantalum (and these are dealt with in the footnotes of Table 9). McLennan and Taylor (1996) revisited the heat-flow constraints on the proportions of mahc and felsic rocks in the Archean crust and revised the proportion of Archean-aged crust to propose a more evolved bulk crust composition. This revised composition is derived from a mixture of 60% Archean cmst (which is a 50 50 mixture of mahc and felsic end-member lithologies), and 40% average-andesite cmst of Taylor (1977). McLennan and Taylor (1996) focused on potassium, thorium, and uranium, and did not provide amended values for other elements, although other incompatible elements will be higher (e.g., rubidium, barium, LREEs) and compatible elements lower in a cmst composition so revised. 

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