Pelopium was the proposed name for a new element found by the chemist Heinrich Rose in 1845.
[1][2][3] The name derived from the Greek king and later god Pelops, son of Tantalus.
During the analysis of the mineral tantalite, he concluded that it does contain an element similar to niobium and tantalum.
The differences between tantalum and niobium and the fact that no other similar element was present were unequivocally demonstrated in 1864 by Christian Wilhelm Blomstrand,[4] and Henri Etienne Sainte-Claire Deville, as well as Louis J. Troost, who determined the formulas of some of the compounds in 1865[4][5] and finally by the Swiss chemist Jean Charles Galissard de Marignac.
[6] This confusion arose from the minimal observed differences between tantalum and niobium.