(1) Samarium is a rare earth element, one of the elements that occupy the space in Row 6 of the periodic table between lanthanum and hafnium .

(2) Gadolinium is a rare earth element, one of the elements that occurs in Row 6 of the periodic table between barium and hafnium .

(3) Titanium is found in column four along with chemically similar zirconium, hafnium , and thorium.

(4) In contrast with tungsten, hafnium does not interact readily with iron-rich material, but it does combine readily with the elements in rocks lacking in iron.

(5) For most of history, hafnium and zirconium were not clearly distinguished from each other.