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Abstract
Refractory metals vary in relative abundance in the Earth's crust from highly abundant like titanium (0.44%) to the least abundant rhenium (1.0 × 10-7%). A major part of these metals occurs as oxides and complex oxides (Ti, V, Cr, Nb, Ta, W), two as sulfides (Mo, Re), and the remaining two (Zr, Hf) as silicates. Due to the lanthanide contraction and being transition metals, some of them have the same atomic radii: Zr-Hf, Nb-Ta, and Mo-W and have very similar properties. Due to these various factors their discovery was extended over nearly a century and half from 1778 for molybdenum to 1924 for rhenium. A review of the historical events that led to their discovery is outlined.