Iron-mass fraction, Fe_planet%, of rocky planets versus the metal-licity [Fe/H] of their host stars. Among the sample of the 48 rocky exoplanets, five super-Mercuries are separated from the others using the different backgrounds (brown and blue), which are drawn by eye. The ODR fitting is performed for the whole sample (dashed lines) and for the sample without the super-Mercuries (solid lines), respectively. Normalized residuals from the fit without super-Mercuries are plotted in the bottom panel.